Resource use in the Parana River Delta (Argentina): moving away from an ecohydrological approach

Claudio R. M. Baigún1,6, Alba Puig2, Priscilla G. Minotti3, Patricia Kandus4, Ruben Quintana4,6, Ricardo Vicari4, Roberto Bo4,

Norberto O. Oldani5,6, John A. Nestler7

AbstractThe Parana Delta region is a huge mosaic of wetlands exhibiting rich biodiversity highly adapted to annual hydrological cycles. In the last decade, however, flow patterns have changed due to the combined effect of dam regulation in the upper basin, water-way construction, new road infrastructure, and climate changes. Such changes trig-gered new strategies for cattle, fisheries, wildlife and forestry uses with associated landscape modifications and are directed to transform the Delta into a productive dry-land area. Such vision fails to envision the value of wetland benefits and environmental services and how traditional resource management can be more sustainable in the long term. We conclude that an ecohydrological template is needed to guide future develop-ment, where economic, social and environmental factors should be harmonized.Key words: floodplain, ecological integrity, flow pulse, environmental goods and services.

1. Introduction

One of the significant features of South America is the enormous extent of wetlands (around one million of square kilometers) which are the largest in the world (McClain 2002). These wetlands are associated with floodplains of the largest rivers (Orinoco, Amazonas, Para-

guay and Parana), having more than 80% of their area in tropical and subtropical humid climates. In the case of low and middle Parana River a large alluvial valley and an extensive delta, which has been considered one of latest well conserved temperate riverscapes. Over the past several years however, historic patterns of water flow start to be disrupted by

Vol. 8No 2-4, 245-2622008

Resource use in the Parana River Delta (Argentina): moving away from an ecohydrological approach?Ecohydrological

Processes and Sustainable Floodplain Management

1IIB-INTECH, Camino de Circunvalación Laguna Km 6, 7130 Chascomús, Argentinae-mail: [email protected]

2Museo Argentino de Ciencias Naturales, Angel Gallardo 470, 1405 Ciudad de Buenos Aires, Argentina

3Universidad CAECE, Dpto. Biología, Junín 516, 1026 Ciudad de Buenos Aires, Argentina

4GIEH, Universidad de Buenos Aires, FCEN, Dpto. Ecología, Genética y Evolución, Ciudad Universitaria, Pabellón II, 1428 Ciudad de Buenos Aires, Argentina

5Centro Científico Tecnológico. Güemes 3450, 3000 Santa Fe, Argentina6Consejo Nacional de Investigaciones Científicas y Tecnológicas

7US Army Engineer Research and Development Center, Vicksburg, Mississippi, USA

DOI:10.2478/v10104-009-0019-7

C. R. M. Baigún et al. 246

hydroelectrical dam regulation located in the upper basin, whereas the construction of 700 km water-way may have modified the natural runoff and shore stability in some narrow river segments of the lower Delta. In turn, new road infrastructure crossing the region appears to have modified the natural drainage within the valley cutting the natu-ral drainage and connectivity between lagoons and secondary channels. Such impacts coupled with climatic changes have promoted new scenarios for live resources and landscape use. Fisheries are probably the most paradigmatic example of such changes. Uncontrolled fishing pressure has produced marked changes in fish stocks and fish assemblages decreasing the size of migratory stock and mean individual length of most important commercial species. In turn disap-pearance of fruit and seed eaters, penetration of marine lineage species and presence of exotic spe-cies could be considered as indicative of environ-mental stress (Quirós 1990). Other activities such as cattle ranching, that has changed from seasonal to permanent (Kandus et al. 2006), and forestry development that is being developed by draining of natural wetlands (Quintana, Kalesnik in press) added to an increase in urban and agriculture pol-lutant inputs reflect the need to start managing the delta natural resources within an ecohy-drological and socioeconomic frame-work. The paucity of scientific informa-tion and the lack of appropriate hydro-logical data have precluded yet for developing a comprehensive model describing and relating how most important ecological processes are cou-pled. Such constraints clearly reduce the ability to support sound management guidelines to conserve living resources in a sustainable way. The aim of this paper is to provide for the first time an overview of the Parana Delta resource problems attempting to present an ecohydrologi-cal perspective (Zalewski et al. 1997). We briefly describe the main exploited resources and their relationship to past and present landscape uses in terms of goods and services, identifying actual and potential threats. We also discuss available tools which can help to change these threats into sustainability opportunities.

2. The Parana Delta Region

The Parana River ranks second in South America after the Amazon, in terms of basin size, length, and water discharge (Neiff et al. 1994). Among

the great rivers of the world, the Parana flows from tropical latitudes to temperate zones, converging with the Uruguay River to form the Rio de la Plata estuary. The Delta region covers over 17 500 km2 on the final 300 km of the Lower Parana (Fig. 1), being completely freshwater. The Parana Delta is considered a wetland macrosystem (Neiff, Malvárez 2004) formed in a littoral complex developed mainly during the last 6000 years despite of some former processes that took place during the Late Pleistocene and early Holocene periods (Iriondo 2004). The evolution of the Delta comprised a fluvial period represent-ed by river flood deposits; a marine ingression with development of a sand barrier, coastal lagoons, minor tributary deltas and estuaries and well-developed regression deposits; an estuarine phase characterized by extensive tidal deposits in the central area; and the present fluvial period, with channel and deltaic deposits advancing into the Rio de la Plata estuary (Iriondo 2004). The current hydrological regime is dominated by floods from the Parana, combined with floods from Gualeguay and Uruguay rivers, tidal and storm surges from the Rio de la Plata estuary and local rainfall events, each with a distinctive hydro-logical signature. Although flow data is lacking for

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Fig. 1. The Parana Delta as seen by the Terra Modis sensor in the blue wavelength on January 16th 2004.

Parana River Delta: moving away from an ecohydrological approach 247

inner Delta branches, analysis of satellite imagery can depict that the flood pulses of the Parana River represent the main flood source in the upper and middle Delta (Fig. 2). However during strong El Niño events the whole Delta is affected. The spa-tial footprint of this ecohydrological complexity can be represented by the zoning schemes of Malvárez (1999) and Kandus et al. (2006), who recognized several distinctive geomorphic units for the whole region and the lower part of the Delta, respectively (Fig. 3). The flood pulse from the Parana River is more irregular than other large South American rivers such as Amazonas or Orinoco (Carignan, Neiff 1992), showing in the Delta several peaks, the main ones being at the end of summer (March) from High Parana river and during winter (June-July) from Paraguay, with low flows typically by the beginning of summer. In the upper Parana high water level period greatly var-ied in length and time among years (Vazzoler et al. 1997) where dam operations have reduced high/

low water hydrometric ranges (Agostinho, Zalewski 1995). Unfortunately no detailed hydrological meas-urements are available for most of the Delta region, particularly for main secondary branches where water level may exhibit important variability accord-ing to geographical location. Delta heterogeneity provides variety of habi-tats for a productive and rich biodiversity and a wealth of ecological services. Marshes are identified as one of the main land cover types of the region and are characterized by a very low richness in plant composition, being dominated by Schoenoplectus californicus (junco) or Scirpus giganteus (corta-dera). In the lower Delta alone marshes cover more than 290 000 ha (Kandus et al. 2006).

3. Provision of goods

Wetlands are been considered very valuable systems due to their high biodiversity and ecologi-

Fig. 2. Comparison of flood sources in the Parana Delta. The shaded area in each map represents the extent of iso-lated flood event for each source as seen by Landsat imagery, allowing to compare their relative importance.


cal functions (Skinner, Zalewski 1995; Tindamanyire 2003). Although the Delta represents a major part of the Parana basin and its importance for biodiversity and resource abundance is well-recognized (Quintana et al. 2002), specific information is still rather poor. However a high diversity of goods, ben-efits and services has been identified in the Delta varying in importance according to different land-scape characteristics and geographical areas (Rosato 1988; Malvárez et al. 1999; Bo, Quintana 1999; Kandus et al. 2006).

Fishing

Fishing has been a traditional activity in the Lower Parana River, this area providing most of commercial catches in the basin. The main target species is sabalo (Prochilodus lin-eatus) (Espinach Ros, Fuentes 2000) which may represent up to 60% of fish biomass in the Middle Parana floodplain lagoons (Bonetto et al. 1970; Tablado et al. 1988). The sabalo fish-ery portrays a noticeable example of changes in resource exploitation, which follows the general trend of overall increase of fishing pressure on target species in the Parana basin. Landing statistics from 1945 to 1984 in the Parana basin showed low to moderate fishing pressure and fish yield, of which 40% of catch consisted of sabalo (Quirós, Cuch 1989),

Victoria being the main landing port. Fishing activities were regulated by seasonal demands. Its use was mainly as fresh food and for oil production, with only 13% allocated for expor-tation (Boivin, Minotti 1990). Most fishermen were part-time, since the fishery was combined with hunting as the basis of the local economy and way of life (Rosato 1988, Malvárez et al. 1999). After 2001, driven by a strong monetary devaluation, a non-regulated industrial fishery developed, the sabalo being exported to diffe-rent Latin American countries. Such activity stimulated the installation of several freezing companies and the entry of new fishermen, the low impact artisanal fishery being displaced by an uncontrolled industrial fishery. Whereas his-torical catch in the area averaged 10 000 to 15 000 tons between 1925 and 1990, after 2001 a rapid increase took place which tripled the catch reaching a peak of 37 000 tons in 2005 (Fig. 4). The increase in fishing effort was clearly paralleled by a dramatic decrease in sabalo mean length, which represented a signal of possible overfishing. These trends coupled with other fishery considerations (see Espinach Ros, Sánchez 2007) supported the idea that sabalo stocks were at risk, encouraging author-ities to impose a total allowable catch of 15 000 tons, its previous historical value, in an attempt to restore the fishery.

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Fig. 3. Landscape units based on Malvárez 1999, Iriondo 2004 and Kandus et al 2006. A: Upper Delta impaired drainage plain B: Old floodplain with large lakes C: Sand barrier and regression ridge deposits D: Old tidal plain E: present day fine meander bar plain F: Predelta coastal lagoons G: Deltaic plains of mainland tributaries H: Ibicuy sand island I: Lower Delta J: Prograding Delta front.


Forestry

Fruit production and poplar forestry (for manufacture of fruit boxes) were the main eco-nomic activities till the 60´s when recurring extraordinary fluvial and tidal floods, combined with severe frosts, wiped out plantations and most of the Delta population moved to mainland cities seeking stable employment (Bó, Quintana 1999; Quintana 2005). In the 70´s, encouraged by pro-vincial governments, forestry plantations of wil-low (Salix) and poplar (Populus) were promoted as the solution for this economical and depopu-lated area, followed by the construction of a paper mill in San Pedro which would meet demands for the main capital city newspapers. The productive peak was reached in 1979 with a total cultivated area of 110 000 hectares (Borodowsky 2006). However the 1982-83 floods again hit this sector, destroying a considerable number of plantations. In the following years, forestry continued to develop inside areas protected from major floods. Forestry for paper pulp production is still the main economic activity at present. Willow plan-tations represent most of the lower Delta land-scape, preferred due to their rapid growth and tol-erance to waterlogged conditions. Poplars require dryer conditions so they are planted on natural levees and inside polders. Nowadays, these spe-cies occupy 58 000 hectares with an 80:20 willow to poplar ratio. Two afforestation modalities are practiced. The open-ditch, practiced by small pro-

ducers, involves the construction of a network of ditches and channels in order to increase the water run-off. Large companies follow a “polder” approach to water level management, where the plantation is totally surrounded by levees to pro-tect trees from floodwaters (Quintana, Kalesnik in press). Forestry activities also include the exploitation of native species like Prosopis nigra or Acacia caven for firewood and fence posts (Quintana et al. 2002).

Cattle ranching

Cattle management was historically per-formed as a seasonal activity taking place during late winter and spring when the river is at the lowest stage (Rosato 1988). Nowadays the sus-tained increase in soy bean prices is expelling beef cattle ranching from traditional mainland areas to marginal ones. The islands along the main Parana channel and Delta are the main receptors of these cattle as most are federal or state public lands, and for its proximity to the most productive country ranching areas located on the Pampean region. This trend has even increased, due to a concurrent dry spell condition with lack of regular floods since 1999 and due to high soy prices in the market stimulating changes in land use and livestock replacement by agricul-tural practices in most productive grassland areas. For the whole region, the head of cattle increased from 160 000 in 1997 up to 1 500 000 in 2007.

Considering just the area sur-rounding the new highway which connects the cities of Victoria and Rosario, cattle increased from 40 000 to 190 000 individuals in the last three years (Belloso 2007), favoring a permanent activity. Manuals of good forestry practices for island forest projects in the lower Delta are encouraging rental contracts with low cattle density for established plantations to reduce chemical weeding.

Hunting

Wildlife hunting is another traditional activity comprising subsistence, com-mercial and sport modalities. It is based mainly on mammals, birds and reptiles (Quintana et al. 1992), varying according to Delta regions. Quintana et al. (2002) for example recognized that 13 mammal species, 10

Fig. 4. Historical catch and mean length from sabalo captures in the lower Parana area, HSY - historical sustainable yield; OF - overfishing (modified from Espinach Ros, Sánchez 2007). Catch data from 1925 to 1987 are records from National Agency of Freshwater Fisheries. Data from 1995 to 2007 cor-responds to Sanitary National Service (SENASA). Mean length values obtained from Vidal (1967), Boivin, Minotti (1990), Dománico, Delfino (1998) and Espinach Ros, Sánchez (2007).


reptiles and amphibian species and 28 bird species could be considered as target species. Their use and exploitation level however differ depending of their commercial, subsistence or sport value. By far the most important target species are the coypu (Myocastor coypus) and the capybara (Hydrochaeris hydrochaeris) which inhabit aquatic and riparian habitats and provide an important protein source for local people, while furs and hides are stored in order to sell them (Bó, Quintana 1999). Unlike most Delta activities, hunting takes place through-out the entire year (Rosato 1988), although there is a hunting calendar for coypu restricted to the May-October period. No doubt, the Delta represents one of the most important hunting area of capybara pro-viding more than 40% of capybara furs (Bo et al. 2005). Just in Entre Rios´s Ibicuy Department (which represents only the 10.6% of the Delta area) more than 400 000 individuals of coypu are annu-ally hunted (Quintana et al. 2002). Hunting is also showing sign of overexploitation as captures are dominated by young individual (Bo et al. 2005).

Other activities

Fruit orchards, sand and peat extractions were traditional activities in the lower Delta until 1960. Most recently apiculture has grown and extended to whole Delta (Rosato 1988; Malvárez et al. 1999). Also ornamental and bait fish cap-ture and culture are minor traditional activities developed in areas closed to main recreational fisheries (Quintana et al. 1992).

4. Environmental services

The Parana Delta still exhibits a good con-servation status and therefore is assumed to pro-vide most environmental services. According to Brinson (2002) the key generic functions are the maintenance of hydrological and biogeochemical cycles, provision of adequate habitats for vegeta-tion, fish and wildlife, as well as biodiversity bio-mass production. However, little information could be gathered and quantified relating such functions to services.

We expect that such characteristics are favora-ble for providing the environmental services identi-fied for wetlands such as flow regulations, ground-water recharge, food patches and breeding grounds for wildlife, water quality improvement, retention of sediments, protection of stream banks from erosion, tourism and recreational activities (Keddy 2000). One of the most significant yet not fully per-ceived wetland benefits are the capacity of seques-tering atmospheric carbon. Wetlands store carbon within their plant biomass instead of releasing it to the atmosphere as carbon dioxide. Typical anaero-bic soils in wetlands increase organic matter half-lives by nearly an order of magnitude over aerobic decomposition in upland ecosystems (Reddy et al. 1986). Information of Delta wetland benefits is only preliminary. Vicari et al. (in press) measured aboveground biomass (AB) and net aboveground primary production (NAPP), comparing marshes to forest plantations. They found out that Salyx babylonica plantations have ten-fold higher above-ground biomass than Scirpus giganteus and Schoenoplectus californicus marshes, but in con-trast, all NAPP for all the land cover types were within the same range (Table I). This means that marshes have better productivity efficiency as they have a much higher (12 to 15 times) production to biomass ratio (NAPP/AB). In turn, at a regional scale, aboveground bio-mass is around nine-folder higher in afforesta-tions than in marshes but accumulated organic matter in soil show the opposite pattern (10.4:1) (Table II). These results demonstrate that the amount of total organic matter accumulated by marshes (107 070 200 Tons) are huge compared to afforestations, representing 91% of total organ-ic matter accumulated. Despite planted trees accumulate considerable organic matter as woody vegetation, this will be lost as they are cut off, whereas marshes are permanent. Another important benefit of unconverted marshlands is their capacity for trapping pol-lutants. Villar et al. (1999) showed that heavy metal content was higher in marsh sediments and aquatic plant rhizomes than in adjacent water. Water quality improvement is also a valuable service strongly related to the possi-

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Land cover-Land use AB

Tons ha year-1 mean ± SD

NAPP Tons ha year

mean ± 1 SD NAPP/AB

Salix babylonica plantation 113.4 15.1 0.13 Scirpus giganteus marsh 10.3 ± 2.4 14.9 ± 3.8 1.5 Schoenoplectus californicus marsh 8.8 ± 0.6 16.5 ± 3.5 1.9

-1 -1-1

Table I. Mean aboveground biomass (AB), net aboveground primary production (NAPP) and production to biomass ratio (NAPP/AB) for Salix babylonica plantation and Scirpus giganteus and Schoenoplectus californicus marshes in the lower Delta of the Parana River (modified from Vicari et al. in press).


bility of using the Delta as a relevant source of drinking water for the northern Buenos Aires conurbation.

5. Impacts, present trends and threats

Man’s activities in the Parana Delta have focused upon generation of goods and economic revenues producing significant threats to wildlife, fish, native vegetation, water quality and land-scape integrity of wetlands.

Infrastructure development: dams, roads and waterways

Infrastructure works in the Delta are diverse and sometimes difficult to assess in terms of impacts. The Rosario-Victoria highway recently constructed was built over large constructed levees across 65 km of the Delta with crossings only for major streams. Dikes, ditches and pol-ders are being built to protect forested lands. In turn, a waterway (Hidrovia Project) constructed on the main Parana branch to allow navigation from the Atlantic Ocean to Rosario port may have still unknown influences on water velocity, sedi-ment transport, adjacent wetlands drainage and bank erosion by navigation. Such effects were predicted for upper Paraguay wetlands (Hamilton 1999; Gottgens et al. 2001). Whereas the Parana River differs in several hydrologic and geomor-phologic respects from the Paraguay River, the dredged channel uses most of the river width in some reaches of the lower Parana Delta, generat-ing intense coastal scouring from large cargo boat passage (Baigun, unpubl.).

Industrial and urban wastes

Population and industries are concentrated in big centers located on the mainland right bank of the Delta between Santa Fe and Buenos Aires cities. Some important industries located in Rosario area release wastes directly to the main channel. In the lower Delta polluted waters from Buenos Aires conurbation may enter through the

Lujan River, which flows to the Rio de la Plata estuary bordering the final Delta, favoured for the complex hydrology of the zone that includes ebb and flow effects (O’Farrell et al. 2002). Lujan River receives agrochemicals as well as domestic and industrial (mostly untreated) effluents, most-ly entering from the Reconquista River, one of the most polluted South American rivers. The lat-ter river showed very high turbidity, phosphorus and dissolved heavy metal concentrations (often exceeding national guideline limits for aquatic life protection) along its course, whereas very high nitrogen concentration as well as very poor dissolved oxygen (often showing anoxia), near its mouth in the Lujan River (Castañé et al. 1998; Olguín et al. 2004). Detected organochloride pes-ticide concentrations were 40 to 400 times the national legal level for water life protection (Rovedatti et al. 2001). Chemical analysis per-formed in the lower Delta (Cataldo et al. 2001; de Cabo et al. 2003) showed that some heavy metals such as Zn, Cu, Cr, Pb, Fe were well above the water quality guidelines for aquatic life. In sedi-ments some polycyclic aromatic hydrocarbons, heavy metals and benzopyren also surpassed guideline levels for protection of aquatic biota (Cataldo et al. 2001). In monitored courses of the lower Delta Escherichia coli concentrations exceeded the standard for recreation activities with different severity, being higher in Lujan River (Table III). This bacterium provides direct unequivocal evidence of fecal contamination with recent sewage or warm-blooded animal wastes, being a good indicator of harmful pathogens, such as Salmonella, Shigella, enteroviruses, Cryptosporidium, and Giardia.

Intensification and expansion of current wetland resource uses

Both types of afforestation (polder and open-ditch methods) have deeply modified the land-scape of the majority of the lower Delta area. Forestry practices vary in their effects on wild-life. Open-ditch plantations appear to have a posi-tive effect on habitat suitability for many wildlife species such as capybara or river otter (Lontra

Landcover type Aboveground

biomass (Tons)

Soil Organic Matter (Tons)

NAPP (Tons km- 2)

Total Organic Matter (Tons)*

Salix spp plantation 9 230 760 10 175 000 927 19 405 760 Scirpus giganteus marsh 653 95 949 560 1 013 349 96 602 580 Schoenoplectus californicus marsh 392 10 075 140 736 10 467 620

Total 9 231 805 116 199 700 1 015 012 126 475 960

Table II. Estimated aboveground biomass, soil organic matter, productivity and total organic matter for each of the landcover types for Scirpus giganteus and Schoenoplectus californicus marshes and Salix spp plantations in the Lower Delta of the Paraná River region. Zones follow Fig. 1.


longicaudis) (Quintana, Kalesnik in press) because the resulting reticulate pattern not only creates more land-water interfaces but also facili-tates matter, energy and species fluxes (Quintana 1999). The intricate network of ditches and chan-nels has apparently benefited capybara as the water corridors enable their access to different resource patches. The establishment of new plant species also expanded capybara trophic resourc-es. Other types of lineal habitat consist of levees running alongside the channels which are mostly used to move agricultural machinery within the forestry plantations. They provide capybara with rich grazing and sheltered resting areas (Quintana 1996). For coypu, channels exhibit good habitat suitability, particularly, those which maintain cer-tain connection with the streams, providing areas for shelter, feeding and resting (Bó, Quintana 1999). By contrast, in the polder afforestations the areas behind the dam are completely drained and the original marshes are eliminated system-atically, so habitats become unsuitable for aquatic and wetlands species due to lack of water-courses and freshwater marsh patches (Quintana, Kalesnik in press). Besides, regular practices involve the removal of native species to avoid competition with saplings for water and nutrients. Also, herbi-cides are starting to be used for controlling native species (Garau et al. 2006; Achinelli et al. 2006) and poisons are frequently used in order to con-trol harmful species like rodents which may affect young trees (Quintana et al. 2002). Local hunting has affected populations of waterfowl, capybara and other highly valued fauna (Bó, Malvárez 1999). Uncontrolled fishing favored by lack of proper mesh regulations and harvest limits have reduced not only sabalo stocks but also other important target species such as dorado (Salminus brasiliensis) and surubi (Pseudoplatystoma corruscans, P. fasciatum), very valuable species for recreational and sport fisheries. Undesirable effects of the sabalo fish-ery have been the expansion of intensive com-mercial fishery in areas where artisanal and rec-reational fishing were previously the only activity (Espinach Ros, Sánchez 2007), and the bycatch of non target species. In turn, the current lack of periodical floods has encouraged a change from seasonal (Malvárez

et al. 1999) to permanent cattle ranching (Kandus et al. 2006). High livestock density also impacts directly on critical habitats for wildlife, changes community structure of vegetation, reduces soil humidity, modifies the chemical composition of the soil, and impacts on water quality. Livestock also competes for food resources with herbivo-rous fauna and removes riparian vegetation. For example, in areas shared by cattle and capybara, the seasonal trophic niche overlap was up to 58% (Quintana et al. 1998). It is also expected that decrease in flood intensity and time extension may affect the fish production impacting on those species such as the sabalo that needs the pota-mophase for a successful growth of juveniles and to sustain the floodplain fishery. Large livestock densities seriously threaten humans, fish and ecosystems, being a source of organic and microbiological (pathogens and para-sites) pollution. Veterinarian products applied to the livestock, as antibiotic substances and hor-mones, may be transferred to the water courses by cattle manure runoff or during flooding events. Manure containing disease-causing pathogens (10 to 100 times more concentrated than in human waste) can reach streams through runoff from field deposition. According to Belloso (2007), the organic wastes produced by 190 000 head of cat-tle grazing in the Victoria-Rosario area may be equivalent to those produced by a city of 4 mil-lion people, but remaining excluded of pollution regulations or impact assessment requirements. In addition cattle and livestock manure represent major methane sources (USEPA 2008), and their effects are potentiated as cattle ranching is mov-ing from seasonal to a year-round activity. Tourist activity has grown steadily, particu-larly in the lower Delta (Quintana 2005). Main impacts may be related to waste and habitat per-turbation by navigation. In turn, urban develop-ment has emerged in the last years as a new phe-nomenon concentrating in the lower Delta area and on the Rosario-Victoria axis. Some of these urban projects advanced on floodplain marshes, promoting their filling or their isolation from main courses by drainage modifications. In addi-tion to habitat fragmentation, other impacts include natural vegetation removal, shore modifi-cation and pollution by wastewaters.

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Values Lower Lujan River

Parana de las Palmas River

Carabelas River

Parana Mini River

Mean 1726 544 280 178 Max 3090 2400 1500 430 % unsafe samples 100 55 36 40

Table III. Concentration of Escherichia coli in water samples (NMP100 cm-3) from four Delta rivers (1 dm3 samples between October 2003 and March 2007, except Lujan: 8 samples since September 2004). Standard for recreation activities: 200 cfu 100 cm-3 Calculated on public data of the San Fernando Municipality.


Alien species represent an increasing threat on native species. Exotic shrubs have invaded disturbed marshes and slopes inside polder plan-tations. Most important aquatic and wildlife inva-sive species are the freshwater molluscs Corbicula largillierti, C. fluminea and Limnoperna fortunei, the Hungarian carp Cyprinus carpio and the exot-ic deer Axis axis (Kalesnik, Quintana 2006).

6. Discussion

South America is the world’s most fluvial continent, supporting an impressive extent of wetlands. Argentina’s large wetlands are not escaping from global trends, starting to show the effects of pervasive anthropic factors such as dik-ing, drainage, eutrophication, water diversion for agriculture, floodplain disconnection, hydrologi-cal changes, dam construction, etc. (Brinson, Malvárez 2002). The Middle and Lower Parana River has been targeted as a reference system due to its natural processes and structural complexity not yet found in most of regulated rivers (Nestler et al. 2007). Thus, it is of critical importance to predict future changes not only based on climate change variables but on land and resource use, together with economic and social policies.

Flood pulses and resource dynamics

As other large rivers, the Parana exhibits a strong dependence on flood pulses (Nestler et al. 2007). Flood pulses are critical components of floodplain river integrity (Poff et al. 1997), trig-gering important ecological features (Junk et al. 1989; Junk, Wantzen 2004). They drive the exchange and storage of organic matter between the floodplain and main channel, and influence biodiversity by producing sea-sonal disturbances (Ward et al. 1999). Nutrients contained in sediments become mobilized as they are dissolved and resuspend-ed, and primary production and decomposition rates change also during flooding (Bayley 1995). In the Parana River dissolved organic carbon (DOC) represents by far the most important carbon source (Depetris, Paolini 1991). As the flood pulse recedes, flood-plain DOC, particulate organic carbon (POC) and nutrients may represent a valuable source for biotic communities becoming a key mechanism for supporting the overall sustainability of the system. Flood pulses may not

only affect organic and inorganic carbon cycles but indirectly stimulate productivity because of high concentrations of suspended solids carrying adsorbed nutrients (Bonetto et al. 1989). Flood pulses in the Parana River have a paramount importance through out the whole basin, not only at the lower and middle floodplains but also in the upper reaches as pointed out by Agostinho et al. (2000, 2004). Moreover Agostinho et al. (2000) described the dynamic changes drived by flood pulses in the last remaining floodplains of the upper Parana River demonstrating how eco-system integrity is highly dependent of pulse per-sistence.

Upper Parana basin effects

Rivers have been envisioned as a sort of interrelated processes that take place along the main axis (Vannote et al. 1980; Sedell et al. 1989) exchanging nutrients and organic matter with their floodplains (Junk et al. 1989). It has been also recognized the critical importance that bio-geochemical processes becomes not disrupted (Elwood et al. 1983). Unfortunately the strong regulation exerted by several large dams in the upper Parana basin represents a major serial dis-continuity (Ward, Stanford 1983), modifying biotic and abiotic processes. The upper Parana basin exhibits at present more than 50 dams, some up to 2250 km2 (Agostinho et al. 2007), and according to Agostinho et al. (2000) the upper Parana is one the most regulated river in the world. Dam construction and impounded sur-face in the Parana basin increased sharply after 1950 (Fig. 5.). Other major factors are however important. Tucci and Clark (1998) noticed that

Fig. 5. Temporal variation of Parana River discharge for different year periods (records from Parana city).


increase in river flow occurred after huge defor-estations and land use changes took place in the upper Parana basin. Bonetto et al. (1989) claimed that extensive deforestation intensified the run-off process and soil erosion, raising suspended solid loads, but at the same time due to the reten-tion by hydropower dams in the upper basin nutrient suspended and dissolved contents have decreased. Additional impacts by dam are related to sediment dynamics by trapping sediment in reservoirs, altering sediment transport capacity downstream and acting as carbon sink. The sedi-ment budget for the Middle Parana River, down-stream of Itaipu and Yacyreta dams decreased up to 80 % since closure of the dams, being compen-sated by increase of sediment transport by the Bermejo River (Amsler et al. 2007). A closer look to the hydrological patterns in the lower basin show that before 1980 the Parana river had a regular cycle with a well defined main flood peak at the end of the summer due to heavy rains in the upper Parana basin and a secondary peak at the end of the fall due to Paraguay influ-ence (Fig. 6). Flow change has been partly attrib-uted to dam regulations in the upper basin. Camilioni and Barros (2000) showed that there was a change in the river discharge annual cycle and its difference between maximum and mini-mum of the Middle and Lower Parana after the early 1980s with respect to the earlier period of 1930–80. A noticeable difference between low and high water periods was evident. However, this regular cycle has changed in recent years, with extreme high and low water levels occurring less frequently (Barros et al. 2006). Clearly for the current period (only 1998-2001 figures avail-able), average monthly values have been below the historical means, which may account for

observed changes in resource uses, as it have been the case for cattle ranching, urban develop-ment and reduction of sabalo recruitment described above.

Macroclimate and microclimate effects

The Parana River, like most South American large rivers, is a heterotrophic system which relies of input of organic matter (McClain 2002). Most of the sediments transported by the Parana River are provided by the Bermejo River, which sup-plies 50%-80 % of suspended sediments (Bonetto 1994; Depetris et al. 2003). In the Lower Parana River, Villar and Bonetto (2000) and Villar et al. (2002) pointed out that extreme high floods favored organic matter retention on the lower Delta floodplain, decreasing its concentration in the main and secondary channels. Particularly, El Niño/Southern Oscillation (ENSO) events can produce big changes in suspended matter in the main channel (Depetris, Kempe 1993). Whereas damming appears to be a negative factor by retaining water and ameliorating flood pulses, in an opposite trend, rainfall and flow increases have been observed in several rivers in De La Plata basin during the last decades (Pasquini, Depetris 2007; Barros et al. 2006). Such behavior has been even more evident during ENSO years as such events represent a major factor influencing flood magnitude (Depetris et al. 1996; Garcia, Mechoso 2005). A strong relationship was demon-strated between precipitation and flow (Krepper, Garcia 2003) and Berbery and Barros (2002) stated that for every 1% change in precipitation, a change slightly over 2% in streamflow is predicted. Because wetlands depend on water permanence which in turn is affected by rainfall or floods, cli-

mate change represents a major com-ponent of future wetland conservation. For the Delta area however, setting hydrological alterations scenarios is a complex matter, as sea level changes should also be expected. The Delta front and area of fluvial influence will be the result of a balance between sedi-ments transported by the Parana River, accretion processes and submergence imposed by new sea levels (Villar et al. 1999). The importance of maintaining Parana floods which appears as the most relevant factor to maintain key ecological processes in most of the Delta region should challenge to devel-op new management policies about water uses and benefits at a basin scale. Unlike other Parana basin areas, future hydrological scenarios for the Delta will result from basin-wide and local rainfall events, flow regulation by

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Fig. 6. Temporal changes of dam number and reservoir area in the Parana basin (adapted from Agostinho et al. 2007).


hydrotechnical works across the basin, sea level increase, sediment dynamics at the delta-estuary interface and tides and wind circulation in the Rio de la Plata estuary.

Effects of Delta landscape modifications on biodiversity and resource sustainability

Hydrology appears to have strong influence on fish recruitment in the Lower Parana area (Espinach Ros, Sanchez 2007), portraying how environmental factors are tightly interrelated with social and economic benefits. Landscape changes in the Delta affect biodiversity resource sustaina-bility mainly by changing aquatic connectivity and thus modifying pulse intensity and timing. Lack of connectivity between floodplain lagoons and sec-ondary channels has its major impact on the sur-vival of fish larvae and juveniles, as has been dem-onstrated by Sverlij et al. (1993). Lack of periodic floods has the effect of reducing the wetted area for wildlife, which implies lost of critical habitats for breeding, reproduction, feeding and resting. Open-ditch afforestation has introduced what could be regarded as positive alterations to the islands’ original landscape. Now, this forestry landscape has a high level of connectivity for these species and the aquatic network which facilitates their access to the foraging, resting and shelter areas. They improve habitat suitability for capybara in terms of larger and better grazing areas, increased percentage of land-water interfaces and the pres-ence of freshwater marsh patches for shelter (Quintana 1999). In turn, coypu uses actively water channels for feeding, reproduction and shelter (Bó, Quintana 1999), and other wildlife species such as dusky-legged guan, a big frugivorous game bird which eats mainly fruits and leaves from alien plant species, is found mainly in patches of mature afforestations and secondary forests located along the rivers (Malzof et al. 2006). However, when forestry activities are carried out behind flood-banks or polders, they drastically reduce habitat suitability for many typical wetland species basi-cally due to the lack of standing water behind the floodbanks. In turn, tourism, industrial and urban development have not been perceived as threats to biodiversity in the Delta, but they strongly contrib-ute to altering water quality. Clearly, successful compatible management of aquatic and wildlife exploitation with other productive activities require a clear idea of which landscape elements and spa-tial configuration must be preserved or improved in order to guarantee the necessary habitats.

Sustainability opportunities

Since the Lower and Middle Parana still offer mostly undisturbed floodplains with no reg-ulations by dams, the Parana Delta provides

unique opportunities for examining how natural functional processes drive large river functioning (Nestler et al. 2007). The current context still provides unique opportunities for examining how the dynamic of natural and man-made ecohydro-logical processes drive large river functioning and how biotic resources are coupled and inter-act. Monitoring schemes and reference sites such as LTER should be developed in collaboration with international water organizations, local authorities and landowners, so databases of suita-ble information. However lack of suitable infor-mation is still limiting the capacity to apply ade-quate management policies to sustain natural resources and to conserve areas which still exhib-it almost natural conditions. We argue that the particular ecological characteristics of the Parana Delta, and its position of still being one of the least- disturbed deltaic systems in the world, merit its proposal as a new site for Long Term Ecological Research. The fact that the Parana Delta is located in the lower portion of a huge basin shared by four countries integrating the sec-ond large basin of the continent (De la Plata basin) clearly represents a major challenge for resource sustainability. As the type and intensity of proximate human land uses increases, the Delta wetland is being subject to consequent changes to its hydrology, nutrient and sediment regimes, and habitat quality. In recent years there is a visible intensification in all main economic activities such as cattle rearing, afforestation and fishing. Increasing loads of chemicals - fertilizers, pesticides - and pathogens from agriculture and livestock, hydrocarbons from fluvial transport, as well as domestic and industrial effluents will con-tribute to water quality degradation and will com-bine with physical habitat fragmentation to poten-tially reduce biodiversity. Unfortunately, current economic development policies are promoting these activities without considering how they might impact upon the Delta ecosystem and how they may affect services and goods provided by the Delta wetlands. Such policies were stimulated just few years ago, by some governmental agen-cies recommending filling and draining lowlands and marshes in order to enhance cattle ranching density without considering environmental costs and benefits of removing them.

Recommended strategies for assessment and management

With the portrayal made here of the Parana Delta, it follows that strategies to assess present and future problems should be develop based on tools encompassing the so called Integrated Water Resources Management (GWP 2000). Such approach is envisioned as having the capability to integrate long term hydrological and ecological


processes as a suitable template for sustainable management and predictive planning at a basin scale (Zalewski 2002), maximizing economic and social benefits without compromising the ecosys-tem integrity and resource sustainability. Understanding the dynamic of ecohydrological processes and how biotic resources are coupled and interact with them become thus a critical step toward conservation of wetland ecosystems and floodplain rivers. Use of an ecohydrological approach may solve what Brinson (2002) called “the parallel universe”, merging descriptive infor-mation of wetland distribution, types, size etc with functional properties. We argue that the productive activities in the Delta cannot be managed as is usually observed in dry grassland areas. The current vision of land-scape management holds the idea that the Delta should be transformed into a dryland productive ecosystem. In the region of major Parana River influence, favored by the decrease of strong floods in the last years, the Delta is being pushing to a “Pampean ecosystem”. This implies convert-ing the wetlands into a dryland which can grow crops such as soybean, wheat, maize and support high cattle densities. In turn, in the area influ-enced by the Rio de la Plata freshwater tides, afforestations and urbanizations are the main landscape transforming activities. This implies changing drainage pattern, polder development and wetland filling. A “Pampean vision” of the Delta fails to envision how wetland benefits and environmental services are strongly related to hydrological and biochemical cycles and tempo-ral landscape changes and how they can be sus-tainable in the long term. Considering that Delta wetland landscapes are still not severely impaired, we urge to adopt a general ecohydrological tem-plate to guide future development, where eco-nomic, social and environmental factors should be harmonized. Although the current resource management situation is clearly moving away from an ecohy-drological approach, we can work with managers by developing tools that could help them to implement a multiuse resource approach based on small to moderate fishery development, low scale cattle, smallholder agriculture and affores-tation which can be applicable without compro-mising natural resources. Moreover, natural hydrological pulses may create a suite of dynamic environmental conditions allowing the combina-tions of different activities. In such context basic steps should be considered for providing first operative management tools for maintaining resource sustainability in the Parana Delta. Information in this area is rather sparse and a major limitation is that it does not account for temporal and spatial processes therefore its appli-cability for integration at large temporal and spa-

tial scales is limited. Examples of the importance of taking into account scale processes are found in the study of de Cabo et al. (2003) who showed that temporal change in water chemical composi-tion was associated with the hydrological regime and the consequent extent of the interaction between the river and the floodplain. These authors noted that highest density of phyto- and zooplankton corresponded to the low water stag-es, whereas the lowest plankton abundance cor-responded to the low temperature. This study portrayed the influence on biological variables of both the hydrologic phase and the seasonality, reflected in the change of temperature (a particu-larly relevant factor in the temperate zone). Also Villar et al. (2002) showed that extreme condi-tions due to ENSO event could strongly modify water quality at a larger scale. A key point to assure future resource sustain-ability is to support management actions applying precautionary ecohydrological principles in the short term, and to develop sound management actions integrating ecosystem conservation and socioeconomic activities in the long term. Whereas precautionary principles such as conserving fluvial corridors, protecting riparian vegetation, allowing free connectivity between watercourses and flood-plains, preserving ecotonal and buffer areas, repre-sent well known concepts and recommended man-agement procedures they are difficult to imple-ment. Application of such principles could be bet-ter supported if economic and social outputs based on goods and benefits derived from well conserved wetlands are contrasted with the consequences of human activities that are producing severe or even irreversible landscape changes such as levees, dikes, water diversion, floodplain development, channelization, drainage modification, soil erosion, pollution, etc. as well as impacts derived from intensive cattle raising, agriculture and forestry. The history of water management shows that typi-cal economic activities in floodplains and the tra-ditional engineering approaches used to support them have failed to take into account potential losses of valuable environmental services provided by fluvial systems. Over-engineering of aquatic systems is evidence of a lack of understanding of ecological processes by environmental managers (Zalewski 2002). An example of the consequences of adopting simple hydrotechnical approach for water management is provided by the hydraulic works fulfilled within a project planned for the Reconquista River. Diversion of most of its flow through the spillway channel into the Lujan River five kilometers upstream from its mouth resulted in the intrusion of polluted waters in a zone of islands of the Delta, causing health problems to resident people who usually extract water from nearby courses for domestic consumption (Suárez, Lombardo 2004).

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Data gathering and integration should take into account temporal and spatial scale processes as well as economic valuation of wetland benefits comparing present mismanagement with renewal and enhancement of traditional sustainable prac-tices. A suitable wetland classification system based on a hydro-geomorphological perspective should be developed as a framework to understand wetland diversity and complexity. As was shown, the Delta exhibits a rich mosaic of heterogeneous patchy landscapes with different dependence of hydrology and interconnected by fluvial corridors with different drainage patterns. We argue that indicator metrics are needed that reflect the eco-logical condition of key wetland habitats and demonstrate maintenance of structural compo-nents and functional processes. Many such indices are being assessed for their suitability as river degradation diagnostics (e.g. Lorenz et al. 1997; Springe et al. 2006). Some promising results have already been obtained in the Reconquista River (Olguín et al. 2004). In this river, integration of complementary approaches for pollution assess-ment (physical/chemical variables, toxicity bio-assays with algae, and bioindicators considering phyto- and zooplankton attributes) enabled a pre-liminary selection of indices and key attributes as potential indicators of the river water quality. Observed plankton changes in this highly polluted river were consistent with biotic responses to chemical stresses reported in Xu et al. (1999), demonstrating that such changes were highly related to a decrease in the ecosystem integrity. Thus monitoring and understanding nutrient and pollutant dynamics provide valuable clues for restoring aquatic ecosystems or prevention of deg-radation of vulnerable areas which might be important for provision of ecological goods and services (Zalewski 2004). Ecological integrity as concept provides the necessary framework for protection of key attributes of wetlands important for provision of social benefits. Such concept is strongly associated to the need to maintain flow regime and its attributes (Poff et al. 1997), thus is of critical importance to acquire better knowledge of hydological characteristics of the Delta at a regional scale and to predict how their modifi-cations could change landscape patterns. Even if natural processes cannot be properly quanti-fied at local scales due to their complexity, regional and landscape indicators based on hydrology, geomorphology, biotic communi-ties, spectral and landscape parameters could be used to describe changes at a regional scale, analyzed and displayed by means of a GIS dataware. This exploratory platform will also allow to evaluate new incoming scenarios, based on climatic and hydrological changes linked to anthropogenic impacts.

Indicator species and functional groups with-in aquatic and wetland communities need to be recognized as key elements since they describe and predict ecosystem trends in terms of structure and processes. Procedures such as PULSO (Neiff 1999; Casco et al. 2005) could provide for exam-ple a suitable tool to diagnose the structure and process related to fluctuating hydrological behav-ior typically of floodplains. It is important that policy and resource managers consider how to assure that key drivers of overall productivity processes, for instance flood pulses, remain pro-tected, in recognition of their value for conserva-tion. Poiani et al. (2000) proposed a framework of geographic domains each maintaining a focal eco-system, with characteristic species and supporting ecological processes and their variability. Interestingly, functional areas allow species con-servation at site, landscape and network scales, being such approach suitable for a heterogeneous region such as the Delta. As we showed previous-ly, since resource use in the Delta varies across different units, and the landscape exhibits diverse patterns due to different geomorphic and hydro-logic processes, such a concept is applicable for assessing how species and habitat should be pro-tected, allowing analysis of biodiversity conserva-tion problems at different scales. The sabalo life cycle is an example of how a functional landscape and network approach can be integrated. This spe-cies encompasses several ecological requirements at different life periods, ranging from patchy and even isolated floodplain lagoons used for feed and juvenile growth to highly connected channels required for adult reproduction and larval disper-sion. In the same vein capybara and coypu popu-lations require regular floods to maintain their ter-ritorial range. Finally, we urge consideration of how new incoming scenarios based on climatic and hydrological changes linked to anthropogenic impacts may threaten overall ecological integrity of the Delta and therefore the valuable goods and natural services it provides.

Acknowledgements

This research was made possible by a grant (PICT 1849/06) from the Agencia Nacional de Promoción Científica y Tecnológica (Argentina).

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Resource use in the Parana River Delta (Argentina): moving away from an ecohydrological approach

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