RIVER RESEARCH AND APPLICATIONS

River Res. Applic. 28: 103–117 (2012)

Published online 23 August 2010 in Wiley Online Library(wileyonlinelibrary.com) DOI: 10.1002/rra.1440

SEASONAL CHANGES OF ABIOTIC AND BIOTIC GRADIENTS DOWNSTREAM AMULTIPLE USE RESERVOIR IN A MEDITERRANEAN RIVER

L. LUCADAMO,a* A. MEZZOTERO,a N. J. VOELZb and L. GALLOa

a Laboratorio di Ecologia Generale ed Applicata, Dipartimento di Ecologia, Universita della Calabria, Cubo 6b, via Pietro Bucci, Arcavacata di Rende,

87036 (CS), Italyb Biology/WSB 262, St. Cloud State University, 720 4th Ave S, St. Cloud, MN 56301, USA

ABSTRACT

The effect of regulated flow regimentation on hydrogeomorphological variables, autochthonous and allochthonous trophic sources andmacroinvertebrates communities of the Mucone River, Calabria (Italy) were studied inMay, August and November 2005 at three studysites.The first site (M1) was located close to the impoundment, the second one (M2) immediately upstream from the first permanent

tributary (Cerreto stream) and the third one (M3) about 1 km downstream from the Cerreto confluence.Our results suggest that hydrogeomorphological gradients already exist in spring but their strongest development, with major

consequences for the lotic biota, take place only with the beginning and ending of the dry season.Reduction of river width, shading due to well preserved riparian alder trees and marked sand deposition in November, were the

variables negatively affecting epilithic microalgae biomass at siteM1. These factors partially relieved at M2 site and becamemuch lessimportant at M3 resulting in the highest levels of autotrophic periphyton production.Coarse particulate organic matter accumulation exhibited an opposite trend due to the lack of discharge peaks at M1, whereas in

November, litter fall removed most differences between stations.In May macrozoobenthic communities of the three stations were relatively similar (reophilous gatherer and scraper taxa). In

November sand accumulation reduced spatial heterogeneity and habitats density close to the Cecita dam promoting settlement ofshredder sand tolerant taxa (Plecoptera: Leuctridae) and a drop of community biodiversity. Flow reactivation, especially after Cerretoconfluence, hindered sand accumulation, favoured autochthonous primary production and increased energy sources for macro-invertebrates. Copyright # 2010 John Wiley & Sons, Ltd.

key words: reservoir; seasonal changes; hydrogeomorphological alterations; macrozoobenthic community; trophic sources

Received 15 January 2010; Revised 23 June 2010; Accepted 7 July 2010

INTRODUCTION

Fluvial environments are characterized from source to

mouth by the presence of abiotic gradients (Illies and

Botosaneanu, 1963; Vannote et al., 1980) with concomitant

modifications of the biotic communities. The main

longitudinal abiotic changes include flow (Gore, 1994;

Lake et al., 1986; Statzner and Higler, 1986), substratum

(Schumm, 1977, 1985; Selby, 1985), form and size of the

riverbed (Rosgen, 1994, 1996) as well as temperature (Illies,

1961, 1962; Vannote and Sweeney, 1980). Modifications

also occur in the sources and amounts of allochthonous and

autochthonous primary production (Vannote et al., 1980;

Giller and Malmqvist, 1998).

The construction of reservoirs and the subsequent flow

regulation alter the natural longitudinal variation of lotic

*Correspondence to: L. Lucadamo, Laboratorio di Ecologia Generale edApplicata, Dipartimento di Ecologia, Universita della Calabria, Cubo 6b,via Pietro Bucci, Arcavacata di Rende, 87036 (CS), Italy.E-mail: lucio.lucadamo@unical.it

Copyright # 2010 John Wiley & Sons, Ltd.

ecosystems (Ward and Stanford, 1983, 1995) and modify the

characteristics of river environments. The type and extent of

those impacts on biotic communities depend mainly on the

use of reservoirs (potable water source, irrigation, industrial,

hydroelectric, fisheries), the frequency with which the water

releases occur downstream from the dam and whether water

is released from the epilimnion or hypolimnion (Perry and

Perry, 1986; Gore et al., 1989; Allan, 1996; Rosenberg et al.,

2000).

Some of the most important downstream consequences

produced by modified releases from an impoundment

include flow below minimum acceptable levels (Stanford

and Ward, 1984) and the deposition of fine sediments (Poff

andWard, 1989; Kondolf andWilcock, 1996; Wilcock et al.,

1996). The latter represents a process that may have serious

negative effects on lotic communities (Wagener and

LaPerriere, 1985; Ryan, 1991; Davies-Colley et al., 1992;

Wood and Armitage, 1997).

River basins in Calabria (Italy) often have a steep

altitudinal gradient because of the region’s orographic

104 L. LUCADAMO ET AL.

characteristics, and the water courses are often regimented

by the presence of dikes and reservoirs. The latter often have

multiple uses (Viceconte, 2004), while a few serve

exclusively for irrigation or electric power production. In

the present research the physical, chemical and biological

characteristics of the Mucone River have been studied in a

stretch downstream from the Cecita Reservoir. Water flow

from the reservoir to the river includes only a very small

leakage from the dam, while more appreciable water

releases occur rarely (generally one or two times per year)

and serve to check the functioning of dam floodgates.

More specifically the goals of this research were, on a

seasonal basis, to: (a) examine any differences for flow or

current velocity and substratum values between a segment

near the dam and others farther downstream (also after the

first permanent tributary); (b) verify whether hydrological

and geomorphological modifications occur together with

changes in the allochthonous and autochthonous primary

production input and (c) study the macrobenthic community

responses, which are associated with those regulated

gradients of abiotic and trophic parameters.

METHODS

Study site

The Mucone River is the most important tributary of the

Crati River, which has the largest catchment area and is the

Figure 1. Study area and sampling

Copyright # 2010 John Wiley & Sons, Ltd.

longest river in Calabria. The Mucone River springs from

Serra Stella (1814m above sea level) in the ‘Sila Grande’

and it is 42.8 km long. The basin (Figure 1) shows a sub-

dendritic pattern with a main channel subdivided into

gradually smaller branches (Panizza, 1988) spreading over

an area of 151.334 km2, with a perimeter measuring

83.719 km. The higher altitude stretches contain granites

and granodiorites. In the mid-reaches micaschist, para-

gneiss with amphibolites, phyllites, marbles and quartzites

are present, while acid granulates and sillimantic with

granites gneiss are found in the lower river basin. The

drainage basin has a low human population density and the

road network is poorly developed. Agriculture takes up 50%

of the area: potatoes and sowable crops are grown in the

upper-middle basin, while in the lower reaches arboriculture

is practiced (vineyards, olive tree groves and other fruit

orchards).

The climate of region of Calabria, where this study was

conducted, like that of many Mediterranean countries (Petts

and Amoros, 1996), are characterized by cold and humid

winters and dry and hot summers. Usually wet season lasts

from the month of November to April–May while dry season

begins at May–June and ends at October (Caloiero, 1980) a

rainy trend resulting in two alternating periods of recharging

and lowering of water table.

In the 1950s, the river was blocked by a concrete dam at

1100m above sea level in order to build a reservoir with a

capacity of 108 million m3. This water is used for irrigating

sites on the Mucone River

River Res. Applic. 28: 103–117 (2012)

DOI: 10.1002/rra

ABIOTIC AND BIOTIC GRADIENTS DOWNSTREAM A RIVER 105

adjacent potato and cereal crop land, as well as the

production of hydro-electric power. With regard to the latter

water is directed into pipes and flows around the study area

to generators located respectively at heights of 480 and

198m above sea level. Only an extremely reduced release

of water consistently originates from the dam (below

minimum acceptable flow) while larger releases occur

once or twice per year to check for proper functioning of

the floodgates. Therefore, most of the flow found down-

stream of the dam comes from groundwater input and

seasonal rains. Apart from the drastic interruption in

ecological connectivity because of the existing dam, the

water course in the stretch immediately downstream from

the reservoir is strongly regulated with development of a

marked deposition process that lasts until flow is once

again reactivated by the progressive inflow. This process is

especially influenced by the first permanent tributary, the

Cerreto, which joins the Mucone River approximately

3.2 km downstream from the impoundment (between

the second and third sampling stations). Vegetation on

the steep slopes consists predominantly of pine trees,

while riparian vegetation are primarily alder trees (Alnus

glutinosa).

Sampling procedures

Three sampling stations (M1, M2 and M3), each with a

length of 90m, were established downstream from the

Cecita Reservoir (Figure 1). All stations have a rhithron

physiognomy, and range in altitude from 1097m a.s.l. (M1)

to 960m a.s.l. (M3). The sampling stations were located 0.9,

3.1 and 4.0 km downstream from the impoundment,

respectively. It was not feasible to place more stations

between M1 and M2 because of the steep sides. However,

the number of sites was considered sufficient for the study of

the regulated gradient.

Physical–chemical parameters were measured at each

site in May, August and November 2005. Current velocity

was measured at a distance of three cm from the riverbed

using a flow meter (Mod. 2030R, General Oceanics).

Discharge was calculated for each riffle using current

velocity, water depth and channel width data. Two litre

samples of water were obtained and brought back to the

laboratory to measure concentrations of ammonium,

nitrite, nitrate, phosphate and suspended solids (APAT-

CNR, 2003). The pH, temperature, conductivity and

dissolved oxygen were measured in the field using

portable probes (Mods. HI 991300 and HI 9143, Hanna

Instruments).

Three substratum replicates were taken also at all sites

each month by means of a cylindrical metallic core

measuring 40 cm in height and 26 cm in diameter.

Substratum was gathered in the core to a depth of 10 cm

Copyright # 2010 John Wiley & Sons, Ltd.

either by hand or by digging with a small shovel, then it was

washed through a series of three sieves (0.063–2.00–

16.0mm; Endecotts Limited). After removing the benthic

substratum, 10 L of water was removed from the core with a

pump to obtain suspended inorganic substratum. This water

was poured through the sieves and gathered in a bucket. A

250ml subsample was taken from the bucket for measuring

the silt–clay fraction. Pebble and cobble sample weights

were measured in the field (using a balance) while the

weights of gravel, sand, and siltþ clay were determined in

the laboratory using an analytic balance (Mod. R200D,

Sartorius) after drying at 1058C for 12 h. Substratum

fractions were expressed in percentage composition, and the

following ratios (weight/weight) were calculated: Pebble-

sþCobbles/Sand [(PþC)/S], PebblesþCobbles/Gravel

[(PþC)/G], Gravel/Sand (G/S), PebblesþCobbles/SiltþClay [(PþC)/(SiþCi)] and Gravel/SiltþClay [G/

(SiþCl)].

Macroinvertebrate, epibenthic microalgal biomass and

coarse particulate organic matter (CPOM) samples were

collected at the same time of hydrogeomorphological and

water-column parameters measurements.

Benthic macroinvertebrates were obtained using a

Surber-type sampler, Mod. N. 12.200 (Scubla, Udine,

Italy), having a 25 cm vertical opening and a sub-

trapezoidal shaped frame with an area of 0.0752m2.

The gathering net used was 60 cm long with a 250mm

mesh. Organisms were separated from substratum in

the field, preserved in 70% alcohol and identified in

the laboratory to family level according to Tachet et al.

(2000) and Sansoni (1988), using a Leica stereomicro-

scope. The following macroinvertebrate parameters

were calculated: type and number of taxa gathered,

relative abundance, dominance—meaning the three

most numerous taxa in the community, percentage

Ephemeroptera, Plecoptera and Trichoptera taxa

(% EPT), the ratio DipteraþOligocheta/the rest of the

community, and Simpson and Shannon indexes.

In order to assess epibenthic microalgal biomass, one

cobble was removed from each riffle and placed in a 5 L

dark plastic bottle with a wide neck containing river water.

The sample was kept in a cooler and then transferred to the

laboratory where epilithic chlorophyll a was measured

(Steinmann and Lamberti, 1996). Three CPOM replicates

were taken at each station using the same core for substrate

collection. The macroscopic vegetable debris (MVD)

(woodþ leaves) was gathered by hand from the core,

while the surface and interstitial smaller organic debris

was sampled by first taking out the substratum contained

in the core with a small shovel, and second by removing

the suspended material with a hand pump. All material

removed from the core was then poured through a 1mm

mesh sieve (Endecotts Limited). The micro detritus

River Res. Applic. 28: 103–117 (2012)

DOI: 10.1002/rra

106 L. LUCADAMO ET AL.

sample was added to the respective macroscopic

component, and both were placed in aluminium foil

that was then folded and placed in numbered plastic

bags. In the laboratory, CPOM samples were dried

at 1108C for 12 h and then ashed in a muffle furnace

(Mod ZB/1, CarloErba Reagents) for 6 h. Dry weights were

determined by using a analytic balance (Mod. R200D,

Sartorius).

Data analysis

All data were normalized prior to statistical analyses

using logarithm transformations (Ln (xþ 1)) except

for CPOM (exponential X0.01) and percentages (arcsin-

rootsquare). Parametric one-way ANOVA, post hoc Tukey

test, Principal Component Analysis (PCA), Detrended

Correspondence Analysis (DCA) and Multiple Response

Permutation Procedured (MRPP) were obtained using either

MINITAB Release 13.2 or PC-ORD 4.

Table I. Average chemical–physical variables values of water-column (

M1

NHþ4 (mgL�1) 32.520 (112.3%)

NO�2 (mgL�1) 2.4 (67.05%)

NO�3 (mgL�1) 138.0 (59.16%)

PO3�4 (mgL�1) 8.2 (33.41%)

% O2 saturation 86.30% (13.49%)pH 7.4 (2.36%)Conductivity (mS cm�1) 171.9 (13.09%)Temperature (8C) 9.8 (59.12%)Average riverbed width (m) 2.42

Table II. Seasonal changes of hydrogeomorphological variables betwee

Dis. Vel. % PþC % Gr % Sa % SþCl (

M1M 0.12 0.40 64.7 23.0 12.1 2� 10�3

A 0.01 0.13 47.4 22.7 29.8 5� 10�3

N 0.03 0.20 14.8 38.7 46.3 14� 10�2

Average 0.05 0.24 42.3 28.1 29.4 7.6� 10�3

M2M 0.35 0.72 60.8 24.5 14.6 18� 10�3

A 0.20 0.52 68.2 20.4 11.3 27� 10�3

N 0.17 0.49 61.8 26.7 11.4 5� 10�3

Average 0.24 0.57 63.6 23.8 12.4 3.1� 10�3

M3M 0.67 0.65 72.2 20.9 6.76 12� 10�3

A 0.38 0.55 67.5 24.9 7.53 75� 10�4

N 0.56 0.71 81.5 13.3 4.81 16� 10�3

Average 0.53 0.63 73.73 19.7 6.36 1.2� 10�3

M, May; A, August; N, November. Dis, Discharge (m3 s�1); Vel (m s�1), Current

Copyright # 2010 John Wiley & Sons, Ltd.

RESULTS

Abiotic parameters and chlorophyll ‘a’

Conductivity and nutrient concentrations were generally

similar across sites, with some elevation of NHþ4 near the

dam and an increase in NO�3 at the farther downstream sites

(Table I). Oxygen saturation never fell below levels that

could be harmful for organisms. Flow and current velocity

increased downstream (Table II). The overall percentage of

pebble/cobble substrate increased downstream from the

impoundment whereas percentage sand decreased (Table II).

Epilithic chlorophyll a values were lowest at M1 and

increased downstream, while CPOM accumulation was

highest at M1, dropped to the lowest levels at M2 and

increased at M3 (Table III).

Figure 2 shows the PCA results performed on hydro-

geomorphological and trophic data from Tables II and III

while Table IV illustrates relative eigenvector values. The

first three axes explained 85.69% of total variance with

coefficient of variation in parentheses, n¼ 3)

M2 M3

16.350 (156.4%) 17.570 (101.7%)

3.9 (42.67%) 2.4 (40.03%)395.9 (91.82%) 274.0 (85.75%)13.9 (32.22%) 9.5 (46.55%)

94.83% (7.15%) 88% (2.49%)7.57 (3.82%) 7.73 (0.77%)

183.53 (18.02%) 168.6 (13.51%)8.8 (68.29%) 9.06 (29.33%)3.11 4.48

n study sites

PþC)/Gr (PþC)/Sa (PþC)/(SþCl) Gr/Sa Gr/(SþCl)

2.91 6.45 28.569 2.15 10.5834.87 2.76 28.762 0.70 5.6400.36 0.48 2.230 1.14 4.7682.713 3.23 19.853 1.33 6.997

2.52 4.37 34.432 1.71 13.5963.58 6.22 30.260 1.80 8.0432.75 7.83 18.170 2.62 6.1752.95 6.14 27.620 2.04 9.271

3.89 16.68 67.439 3.81 21.3705.35 13.07 99.437 3.34 57.5928.81 38.91 66.735 3.81 7.8896.01 22.88 77.870 3.65 28.950

Velocity. PþC, PebbleþCobble; Gr, Gravel; Sa, Sand; SþCl, SiltþClay.

River Res. Applic. 28: 103–117 (2012)

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Table III. Seasonal changes in macroinvertebrate trophic sourcesat the study sites

Chlorophyll a(mg cm�2)

CPOM(g surface sampler�1)

M1May 0.832 26.41August 0.142 10.97November 0.206 14.32Average 0.393 17.23

M2May 1.392 0.630August 0.379 1.283November 0.234 9.312Average 0.668 3.741

M3May 6.372 0.133August 0.604 5.123November 1.594 23.85Average 2.856 9.702

Table IV. Loadings of abiotic variables used to perform principalcomponent analysis

Variables Eigenvector

Axis 1 Axis 2

Chlorophyll �0.2505 0.3460CPOM 0.1905 �0.3735Discharge �0.3125 0.1849Velocity �0.2783 0.1745% PþC �0.3226 �0.2090% Gr 0.2036 0.3819% Sa 0.3395 0.2008% SþCl 0.2971 0.1169PþC/Sa �0.3385 �0.2374PþC/Gr �0.2880 �0.3417Gr/Sa �0.2832 0.0171PþC/SþCl �0.2505 0.3460Gr/SþCl 0.1905 �0.3735

ABIOTIC AND BIOTIC GRADIENTS DOWNSTREAM A RIVER 107

53.97% of variance associated with axis 1 and 21.81% with

the second axis. The position of sampling dates in the PCA

diagram suggests that the main ordination was due to

temporal differences in velocity, flow and substrate between

upstream and downstream stations whereas differences in

trophic sources (peaks in epibenthic chlorophyll ‘a’ at M2

and M3 spring dates and in CPOM at M1 spring date) give a

secondary contribution. MRPP application on abiotic

variables database suggest that this trend is consistent. In

fact when the two null hypotheses of no differences due to

Figure 2. Results from the PCA using physical–chemical and trophic variables sho(s¼ sample; n¼ replicates, where 1, 2, 3¼April, 4, 5, 6¼August and 7, 8, 9¼No

journal/r

Copyright # 2010 John Wiley & Sons, Ltd.

space (group definition: distance from dam) and due to time

(group definition: months) were tested in both cases the T-

statistic (Tables V and VI) showed negative values and the

chance-corrected within group agreement (A) was between

0 and 1 and always extremely significant.

Results from the ‘between-stations’ ANOVA performed

on both hydrogeomorphological and trophic data

(Table VIII) were similar to those obtained with multivariate

analysis while ‘between-months’ ANOVAs were not ever

statistically significant (Table IX).

wing sampling date replicates (n¼ 27) for each study site (M1, M2 andM3).vember). This figure is available in colour online at wileyonlinelibrary.com/ra

River Res. Applic. 28: 103–117 (2012)

DOI: 10.1002/rra

Table V. Multiple Response Permutation Procedures (MRPP) results: null hypothesis tested: no difference due to distance from dam(between stations)

Variables Groups Averagedistance

Weighting option Distancemeasure

Test statistic:T

Chance-correctedwithin-groupagreement, A

Probability of asmaller or

equal delta, p

Group definition: distance from damAbioticparameters(same of PCA)

M1 0.0778 C(I)¼ n(I)/sum(n(I)) Sorensen(Bray–Curtis)

�7.4844452 0.19870360 0.00001761

M2 0.0513M3 0.0853

Families(same of DCA)

M1 0.5740 C(I)¼ n(I)/sum(n(I)) Sorensen(Bray–Curtis)

�4.4976704 0.05761969 0.00101972

M2 0.4826M3 0.4257

Each group made of all seasonal samples (May, August, November) per station (M1, M2 and M3). The abiotic (trophic and hydrogeomorphological) and biotic(macrozoobenthic families) variables are the same of PCA and DCA.

108 L. LUCADAMO ET AL.

Differences among study sites in both discharge and

current velocity were statistically significant during August

and November, when strong reduction in rainfall frequency

exacerbated hydrological segregation between the site

closest to the dam and sites farther downstream. However,

the best reactivation of discharge seems to take place only

after inflow of the Cerreto tributary (upstream from M3)

(Table II).

Percentages of the pebbleþ cobble fraction and sand

showed an inverse trend (Table II) fromMay to November at

station M1 with a progressive reduction of the amount of

coarse units in the substrate samples and a constant increase

in sand. The same variables at stations M2 and M3 did not

show an evident trend (Table II) and in November both were

significantly different from M1 values (Table VIII).

The coarse/fine substrate ratios were only significantly

different between sites M1 and M3. The [(pebbleþ cobble)/

Table VI. Multiple Response Permutation Procedures (MRPP) results: nu

Variables Groups Averagedistance

Weighting option D

Group definition: monthsAbioticparameters(same of PCA)

May 0.0721 C(I)¼ n(I)/sum(n(I)) Sor(Br

August 0.0760November 0.0944

Families(same of DCA)

May 0.4798 C(I)¼ n(I)/sum(n(I)) Sor(Br

August 0.4208November 0.4029

Each group made of all station samples (M1,M2 and M3) per month (May, Augus(macrozoobenthic families) variables are the same of PCA and DCA.

Copyright # 2010 John Wiley & Sons, Ltd.

sand] ratios in November at M1 and M3 were the lowest and

highest measured, respectively, for the study period

(Table VIII). Although the [(pebbleþ cobble)/(clayþ silt)]

ratio values also showed significant differences for two out

of three comparisons (Table VII), the clayþ silt fraction

being, on average, only 0.4% of the substrate samples

suggesting a modest role in structuring colonizable niches.

Epilithic chlorophyll density in May exhibited a

significant progressive increase going from the site nearest

the impoundment to the farthest downstream station

(Tables III and VIII), a result consistent with the PCA.

However, in November a secondary peak developed only at

station M3 was significantly different (Table VIII) from the

values measured at M1 and M2, whereas segregation of fall

dates along the second ordination axis was weak.

CPOM accumulation displayed a reverse trend in May

compared to epibenthic chlorophyll. In November, due to

ll hypothesis tested: no difference due to months (between months)

istancemeasure

Test statistic:T

Chance-correctedwithin-groupagreement, A

Probability of asmaller or

equal delta, p

ensenay–Curtis)

�3.5301336 0.09372107 0.00574771

ensenay–Curtis)

�13.367068 0.17124561 0.00000000

t, November). The abiotic (trophic and hydrogeomorphological) and biotic

River Res. Applic. 28: 103–117 (2012)

DOI: 10.1002/rra

Table VII. Macrobenthic communities variables (average values except taxonomic richness) measured during the study period

M.A. T.R. T.D. D.þO./R.O. % EPT Simpson index Shannon index Dominance(�)% HEP. % BAE. % LEU.

M1M 21 13 7.2 0.145 85.91 0.728 0.680 38.68 17.13 1.08A 35.5 16 9.5 1.217 48.41 0.809 0.831 29.90 6.33 19.96N 136.5 15 9.0 0.382 72.89 0.526 0.509 3.05 1.76 64.25Average 64.33 14.66 8.566 0.581 69.07 0.687 0.673 23.87 8.406 28.43

M2M 49 13 8.0 0.235 80.20 0.783 0.753 9.67 30.37 1.51A 226 22 13.0 0.557 64.41 0.769 0.778 10.16 19.74 29.18N 158.7 19 14.0 0.562 58.13 0.804 0.868 14.95 6.67 26.17Average 144.5 18 11.66 0.451 67.58 0.785 0.799 11.59 18.92 18.95

M3M 121.5 20 11.7 0.332 76.36 0.807 0.833 26.63 20.56 0.74A 101.7 16 11.5 0.987 52.08 0.843 0.899 15.51 15.08 6.85N 121.2 23 13.5 0.577 63.38 0.790 0.873 29.66 7.48 12.3Average 114.8 19.66 12.23 0.632 63.94 0.813 0.868 23.93 14.37 6.63

M, May; A, August; N, November. M.A., Macrobenthos Abundance; T.R., Taxonomic Richness (total number of Families per sampling date); T.D., TaxonomicDensities (Number of families found in each replicate, 0.0752m2); D.þO./R.O., DipteraþOligochaeta/Remaining Organisms; % EPT, representation ofEphemeroptera; Plecoptera and Trichoptera within the macrobenthic community; Dominance�, Three taxa with the highest average representation during theentire study; % HEP, Heptageniidae percentage; % BAE, Baetidae percentage; % LEU, Leuctridae percentage.

Table VIII. Results of the one-way ANOVA performed on monthly values of hydrogeomorphological, trophic and macrozoobenthiccommunity data

Parameters May August November

F p SSD F p SSD F p SSD

Between-stations ANOVA (month per month)Discharge 4.32 0.069 — 32.18 0.001 2, 3> 1 3> 2 10.24 0.012 3> 1, 2Current velocity 1.450 0.307 — 15.15 0.005 2, 3> 1 34.51 0.001 2, 3> 1Chlorophyll a 80.70 0.000 3> 1, 2 2> 1 6.24 0.020 3> 1 5.59 0.026 3> 1, 2CPOM 29.28 0.001 1> 2, 3 9.52 0.014 1> 2 0.120 0.891 —% PebbleþCooble 1.19 0.367 — 0.71 0.528 — 13.25 0.006 2, 3> 1% Gravel 0.38 0.700 — 0.03 0.975 — 4.02 0.078 —% Sand 2.27 0.185 — 4.92 0.054 — 9.25 0.015 1> 2, 3% Clay–Silt 3.84 0.084 — 1.65 0.268 — 2.96 0.127 —(PebbleþCobble)/Sand 2.20 0.192 — 2.59 0.154 — 8.46 0.018 3> 1(PebbleþCobble)/Gravel 0.76 0.507 — 0.04 0.964 — 8.78 0.017 —Gravel/Sand 3.76 0.088 — 7.33 0.024 3> 1 3.97 0.080 —(PebbleþCobble)/Clay–Silt 6.08 0.036 3> 1 2.11 0.202 — 6.44 0.032 3> 1Gravel/(Clay–Silt) 1.12 0.387 — 3.07 0.121 — 1.04 0.409 —Macrobenthic Abundance 12.51 0.003 3> 1 6.95 0.015 2> 1 0.52 0.613 —Taxonomic Richness — — — — — — — — —Taxonomic Density 3.18 0.090 — 1.21 0.341 — 12.38 0.003 2, 3> 1DipteraþOligochaeta/Remaining

Organisms0.82 0.470 — 0.71 0.519 — 0.49 0.629 —

% E.P.T. 0.76 0.497 — 1.02 0.397 — 1.66 0.243 —Simpson index 1.77 0.226 — 2.95 0.103 — 9.09 0.007 2, 3> 1Shannon index 1.78 0.224 — 1.65 0.246 — 13.63 0.002 2, 3> 1% Heptageniidae 6.20 0.020 1> 2 0.58 0.582 — 5.80 0.024 3> 1% Baetidae 1.70 0.237 — 3.94 0.059 — 4.57 0.043 3> 1% Leuctridae 0.21 0.818 — 2.64 0.125 — 12.31 0.003 1> 2, 3

SSD, statistically significant differences (Tukey-test). 1, 2 and 3 are for M1, M2 and M3, respectively

Copyright # 2010 John Wiley & Sons, Ltd. River Res. Applic. 28: 103–117 (2012)

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ABIOTIC AND BIOTIC GRADIENTS DOWNSTREAM A RIVER 109

Table IX. Results of the one-way ANOVA performed on station values averaged on a monthly ground of hydrogeomorphological, trophic andmacrozoobenthic community data

Parameters F p SSD

Between-months ANOVADischarge 0.42 0.675 —Current velocity 0.53 0.616 —Chlorophyll a 2.65 0.150 —CPOM 1.38 0.322 —% PebbleþCooble 0.26 0.777 —% Gravel 0.18 0.840 —% Sand 0.19 0.828 —% Clay–Silt 1.42> 0.312 —(PebbleþCobble)/Sand 0.06 0.942 —(PebbleþCobble)/Gravel 0.17 0.850 —Gravel/Sand 0.29 0.755 —(PebbleþCobble)/Clay–Silt 1.01 0.419 —Gravel/(Clay–Silt) 1.90 0.229 —Macrobenthic Abundance 1.44 0.307 —Taxonomic Richness 2.74 0.142 —Taxonomic Density 0.85 0.753 —DipteraþOligochaeta/Remaining Organisms 10.55 0.011 August>May% E.P.T. 10.39 0.011 May>AugustSimpson index 0.87 0.467 —Shannon index 0.40 0.685 —% Heptageniidae 0.44 0.665 —% Baetidae 3.75 0.088 —% Leuctridae 6.07 0.036 November>May

SSD, statistically significant differences (Tukey-test).

110 L. LUCADAMO ET AL.

litterfall, woody and leafy detritus (mostly from deciduous

trees) amounts were comparable between the three study

sites (Table III), a result confirmed by both ANOVA

(Table VIII) and PCA (Figure 2).

Macrozoobenthic parameters

Analysis of the macrobenthic community general

descriptors (Tables VII–IX) suggested that the main

differences along the study transect developed on a seasonal

basis. Six out of 10 biotic parameters were significantly

different in November. In particular taxonomic density and

both diversity indexes were notably higher at downstream

stations than at the station close to the Mucone dam. The

reverse happened for percentage Leuctridae while Hepta-

geniidae and Baetidae percentages were higher at M3 than at

M1. Interestingly the percentage Heptageniidae showed a

significant difference also in May with M1 exhibiting the

highest value for all measurements recorded (Tables VII

and VIII), however it must be emphasized that this

percentage refers to a very low value of abundance so that

its ecological meaning is modest. On the other hand, during

November Baetidae percentages at both M1 and M2 reflect

relatively high abundance values but this taxon displayed a

constant numerical reduction from May to November when

Copyright # 2010 John Wiley & Sons, Ltd.

it reached the lowest level (Table VII). Therefore, this trend

was probably more ecologically relevant versus the observed

difference in fall. The only other macrobenthic variable

displaying a positive ANOVA result was total macrobenthic

abundance (Table VIII). During May at the site downstream

from the Cerreto inflow (M3) total abundance values were

5.78 and 2.47 fold higher than at M1 and M2, respectively,

whereas in August abundance at M2 reached the highest

peak for the entire study (6.36 and 2.22 fold higher than at

M1 and M3, respectively; see Table VII for raw data).

Only three community parameters showed significant

differences when performing a ‘between-months’ ANOVA:

DipteraþOligochaeta/Remaing Organisms (August>May),

% EPT (May>August) and % Leuctriidae (Novem-

ber>May). Due to the lack of significance of the differences

of the first two parameters when performing a ‘between

stations’ (month per month) ANOVA this suggests that their

seasonal variation takes place along the ‘whole transect’

despite to the hydrogeomorphological and trophic gradients

developing downstream the impoundement.

Figures 3 and 4 illustrate the results for the detrended

correspondence analysis performed with taxa having a

representation higher than 1% in the total samples. The

length of the gradient associated with the first three axes

indicated about 50% taxa substitution (taxa turnover; Mc

River Res. Applic. 28: 103–117 (2012)

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Figure 3. DCA plot showing ordination of taxa with a representation higher than 1% (station sampling dates—triangles inside black rectangle—are notdisplayed because they were not distinguishable). Families are indicated with the first eight letters

ABIOTIC AND BIOTIC GRADIENTS DOWNSTREAM A RIVER 111

Cune and Grace, 2002). Coefficients of determination for the

correlations between ordination distances and distances in

the original n-dimensional space were very good, with axes

1, 2 and 3 having R2 values of 57.7, 9.1 and 7.7%,

respectively. Three clusters are evident in Figure 3, one on

the right side of axis 1 including all spring dates for the three

sites and two on the left side of axis 1 whose separation takes

place along axis 2. The lower grouping along axis 2 includes

5 M1 samples (3 fall and 2 summer dates) and 1 fall sample

for M2 (m2s10) while the upper cluster includes remaining

sampling dates.

The DCA results confirmed that seasonal change (axis 1)

was the main factor promoting taxa and site ordination, and

differences in taxa composition among sites (ordination due

to space effect) developed only from the spring to summer–

fall period (axis 2). Families associated with the spring

cluster were reophilous taxa (Simuliidae, Rhyacophilidae,

Limnephilidae, Perlodidae) and microalgae consumers

(Ephemerellidae, Taenyopterigidae). Taxa associated

Copyright # 2010 John Wiley & Sons, Ltd.

with the summer–fall M1 cluster included reophilous/

limnophilous woody debris eaters (Leuctridae, Nemour-

idae), sediment tolerant (Leuctridae, Lumbriculidae) and

low oxygen concentration tolerant (Nemouridae) organisms.

The M2/M3 summer–fall DCA cluster also included

reophilous/limnophilous families, as well as two strictly

reophilous periphyton consumer taxa (Ancylidae and

Heptageniidae) and CPOM consumers (Sericostomatidae).

Baetidae and Heptageniidae families showed a relatively

intermediate position along axis 1 due to their constant

presence in the sites during the study period, and an

intermediate-upper position along DCA axis 2 consistent

with their higher representation during November in stations

far from the impoundment compared to the site close to

the dam.

Once again, MRPP results support the ordination data

(Tables V and VI). The same two null hypotheses used for

PCA: no differences due to space (group definition: distance

from dam) and due to time (group definition: months) were

River Res. Applic. 28: 103–117 (2012)

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Figure 4. DCA plot showing ordination of study site sampling dates (black rectangle inside the plot of taxa; s¼ sample; n¼ replicates, where 1, 2, 3¼April, 4,5, 6¼August and 7, 8, 9¼November). This figure is available in colour online at wileyonlinelibrary.com/journal/rra

112 L. LUCADAMO ET AL.

tested. T-statistic showed negative values and the chance-

corrected within group agreement (A) was between 0 and 1

and always extremely significant. However, the result was

particularly striking when months were used as ‘factors’

suggesting that very strong changes in macrozoobenthic

community take place downstream the impoundment on

monthly (seasonal) ground.

DISCUSSION

The results of mineral nitrogen forms and conductivity do

not support the development of a spatial trend through the

experimental transect due to their high standard deviation

values and lack of substrate oxygen measurements and, on

the whole, they appear to be consistent with both catchment

characteristics (Omernik, 1977) and river physiognomy

(Ghetti, 1997).

The comparable velocity values registered in May among

the study sites were probably due to spring rain falls and to

the melting of snowfields that resulted in a recharging of the

water table that ameliorated the effect of flow interruption

due to the dam. In August when rain contributions were

strongly reduced a drastic decrease in discharge and current

velocity took place at the site closest to the reservoir.

Copyright # 2010 John Wiley & Sons, Ltd.

Flow resurgences downstream (even though in a low-flow

period), especially from the Cerreto tributary, supported the

Mucone River flow causing a strong segregation in

hydrologic regimes between the areas near and farther

downstream from the impoundment. The Cerreto contri-

bution was evident from the significant discharge differences

observed betweenM2 andM3 despite the comparable values

of current (which may be due to similar local slopes).

In November, rain began to increase both in frequency and

intensity and this reactivated the flow in the segment

downstream from the Cerreto tributary, but not at sites M1

and M2. The increase in current velocity at M3 probably

depends on the raising of the water level so that the substrate

friction effect on upper water strata becomes reduced

allowing for faster current near the surface (Hynes, 1970).

The hydrological variable results suggested that although in

spring the dam generates a difference in current and flow

between site M1 and sites M2/M3 it was only when

precipitation was strongly reduced that the regimentation

effect enhanced the development of a marked gradient.

The progressive increase of sand along with the constant

decrease of both pebbleþ cobble fractions and ratios

between coarse substrates and sand at M1 suggest the

burial, on a seasonal basis, of coarse substrate due to fine

sediment (<2mm) accumulation that, in turn, promotes

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ABIOTIC AND BIOTIC GRADIENTS DOWNSTREAM A RIVER 113

embeddedness of the riverbed. This is a phenomenon well

known for depressing biological colonization (Lenat et al.,

1981; Gordon et al., 2004). Differences in substrate

variables between the site close to the dam (M1) and the

site with the best flow reactivation (M3) became striking

in November, when flow and current velocity segregation

persisted from August. The site immediately upstream from

the Cerreto inflow (M2) seemed to occupy an intermediate

position as indicated by the [(pebbleþ cobble)/sand] ratio

that was not significantly different from either M1 or M3.

Such a result may be due to both weaker discharge values

and the physiognomy of M2 which has a tight succession of

small falls that could break flow, increase turbulence and

promote deposition of small particles like sand (Stevenson,

1983). The seasonal trends for substrate corresponded well

with the hydrological trends strongly supporting the idea

that interaction between local climate and the regimentation

effect of the dam results, on a scale of kilometres as for our

work, in a reversal of the natural substrate gradient on a

catchment scale, according to the hypothesis developed

by Ward and Stanford (1983) about one of the effects of

impoundments on lotic ecosystems.

The shading produced by the well-preserved riparian

canopy (Lowe et al., 1986; Hill and Knight, 1988), together

with the average phosphorous values typical of oligotrophic

environments (Dodds et al., 2002), resulted in modest micro-

algal accrual values, except for the peak reached inMay atM3

(Biggs, 1996). Station M3 showed the highest average values

for chlorophyll a (Table III) probably due to a concurrence

between a greater substratum stability (pebbles and cobbles)

favouring colonization and epi-benthic micro-algae perma-

nence (Allan, 1996), and a greater average channel width,

which allowed a better irradiation of the riverbed (Tank and

Dodds, 2003; Ambrose andWilzbach, 2004). The differences

shown in the trimester confirms and strengthens such an

interpretation. In May, before canopy closure, chlorophyll a

showed progressively increasing values going from M1 to

M3, likely resulting from an irradiation gradient. In August, a

generalized reduction of chlorophyll a levels was evident.

These results were likely due to the high shading effect from

canopy closure and perhaps fine sediment accumulation that

could cover the algal microlayer (Brookes, 1986; Graham,

1990; Yamada and Nakamura, 2002), likely hindering light

penetration or making nutrient and gas exchanges more

difficult. In November, defoliation allowed for increased

riverbed irradiation which could potentially stimulate

epibenthic algal growth (Sumner and Fisher, 1979). A result,

however, that was only registered at M3. The high sand

deposition presumably depressed algal development at M1,

while at M2 the combined effect of sand deposition (though

less than at M1) along with a marked increase in cloudy days

compared to spring (ARPACAL, 2009) would hinder growth

of epilithic microalgae.

Copyright # 2010 John Wiley & Sons, Ltd.

Deciduous leaf and wood debris accumulation was higher

near the impoundment whereas lower quantities were

collected at both downstream stations (Table III). It is

reasonable to speculate that the large CPOM differences

detected in May (Table VII) were due to flow abatement

caused by the dam that eliminated discharge peaks, a process

that together with riverbed width reduction promoted CPOM

accumulation close to the reservoir. Studies by Stanford and

Ward (1984) and D’Ercole (1989) concur with our study

while others found increasing CPOM levels with greater

downstream distance from impoundments (Voelz and Ward,

1990; Cortes et al., 1998). These differences are probably

ascribable to the different ways of operating the reservoirs or

different placement of sampling stations (e.g. closer to the

reservoir so that building of the dam could have altered

the riparian environment).

CPOM quantities collected at M1 in August were

considerably lower than those collected in May. It is

difficult to associate this reduction completely with

decomposition (Spanhoff and Meyer, 2004) especially

because in our work no distinction was made between

woody and leafy litter. However, most CPOM consisted of

deciduous leaves and because Alder leaves (a common tree

along the study reach) have a low C:N ratio (Haeckel et al.,

1973), a chemical property that strongly promotes plant

tissue decomposition, while wood has a much higher C:N

ratio (200�>1000:1), we may suppose that microbial

decomposition of CPOMwas appreciable and contributed to

the negative recovery trend between May and August.

In November, when litter fall occurs, the CPOM amounts

collected at the three stations were comparable (Table VII).

However, despite flow reactivation the largest quantities

were observed at M3, probably due to the higher retention

capacity of the river segment as suggested by the greater

pebbleþ cobble sediment fraction (Naiman, 1982).

In addition, the macrobenthic invertebrate community

characteristics appeared to result from the hydrological

regimentation caused by the dam and were further

influenced by the seasonal change of climate. In May,

when flow was still activated primarily by rainfall, drift was

presumably the main factor driving colonization of the

riverbed (Waters, 1972). However, site M1 (mostly) and site

M2 to a lesser extent likely could not rely on this process,

due to dam barrier (Nichols et al. 2006), whereas M3 was

influenced by macroinvertebrate sources ensured by the

Cerreto tributary. Also in August the Cerreto could play a

key-role in determining the abundance of macroinverte-

brates at M3. In fact the highest macroinvertebrate

abundance for the entire study period was observed at

M2, the station nearest to the Cerreto confluence. Many lotic

insects in Italian and other European rivers emerge around

that time of the year (Cummins, 1974; Cattaneo et al., 2006;

Sporka et al., 2006). Due to different placements and

River Res. Applic. 28: 103–117 (2012)

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114 L. LUCADAMO ET AL.

distances of M2 and M3 with respect to the Cerreto inflow,

we may presume that aerial dispersal of adults (Gray and

Fisher, 1981; Cushing and Gaines, 1989) coming mainly

from the Cerreto, enhances the colonization of the Mucone

River at both M2 and M3, with drift processes taking a

secondary role at M2. In November when the flow

reactivates, drift should again be a critical process in

determining composition and abundance of macrobenthos

but we found no differences among the three sites.

Looking at the structure of macrobenthic communities

and especially the timing of dominance by the Leuctridae

across the stations, we may hypothesize that this family

probably colonizes site M1 partly by upstream movement of

the larvae (Williams and Hynes, 1976; Erman, 1986;

Delucchi, 1989; Freilich, 1991). Such a process could

counterbalance drift eliminating differences in abundance

between sites. Autumn litter deposition presumably pro-

motes Leuctridae colonization also at M2 andM3 (Table IX)

as indicated by their increase in abundance from May to

November.

The abundance of the other dominant taxon, the

Heptageniidae, exhibited a trend that matched the seasonal

variation of epibenthic microalgae biomass at M3 (Merritt

and Cummins, 1996) but not at M2 probably due to the lower

level of epilithic primary production. The percentage of

Heptageniidae in the macrobenthic community suffered the

strongest reduction at M1 in November probably as a

consequence of their intolerance to fine sediment deposition

(Relyea et al., 2000) and depressed level of autotrophic

periphyton.

In all three sites the representation of Baetidae

progressively reduced going from May to November. This

trend suggests that other factors not taken into account in

this work, rather than the hydrogeomorphological gradient,

controlled their seasonal variation along the study transect.

Differences in taxonomic richness among stations were

not particularly high suggesting that the total number of

niches per site was not greatly affected by the flow

regimentation (Cortes et al. 2002) and subsequent sand

accumulation, perhaps because of high total spatial

heterogeneity. On the contrary the density of niches, that

is the spatial diversity measured at a microscale (the surface

of the sampler), not only was consistently lower at M1 than

at M2 or M3 (perhaps due to interruption of ecological

connectivity) but also showed a significant difference in

November between the upstream and downstream sites,

when sand became the dominant component of the riverbed

at M1. It is well know that pebbles and cobbles separately as

well as in mixture enhance the richness of macrobenthic

communities (Mackay and Kalff, 1969; Tolkamp, 1980;

Reice, 1980; Minshall, 1984) whereas sand deposition and

its filling of crevices depresses invertebrate colonization

both reducing space available (Waters, 1995) and lowering

Copyright # 2010 John Wiley & Sons, Ltd.

substrate oxygenation especially when high levels of organic

substrate are present (Ryan, 1991), as in the case of site M1

due to CPOM accumulation. Invertebrate responses consist

of increased drift activity (Culp et al., 1986) of non-tolerant

taxa while covering of substrate with fine sediments

hinders colonization by upstream movements (Luedtke

and Brusven, 1976).

Consistent with the extreme dominance of only one

family (Leuctridae) at site M1 in November and con-

comitant with the low taxonomic density, both promoted by

impairment of the physical–chemical characteristics of the

lotic environment and accumulation of CPOM, biological

diversity (measured by Simpson and Shannon indexes) was

greatly reduced, a result common to other studies on

damming effects (Pardo et al., 1998; Sagawa et al., 2004;

Takao et al., 2008). Data existing in the literature indicate

different fine sediment deposition thresholds above which

biodiversity alteration in the macrobenthic community takes

place. A study by Relyea et al. (2000) sets this sediment

deposition threshold around 25–30%, while Spindler (2004)

suggested between 40 and 50%. Our work seems to be in

accordance with the latter, in as much as when the sand

percentage in August at M1 reached a value of about 30% no

differences in biodiversity levels were detected between

upstream and downstream stations. In November when

the sand percentage at M1 equalled 45% a statistically

significant difference was observed between M1 and sites

M2/M3 for biodiversity indexes and dominance. Many

studies support the idea that deposition of fine sediment

changes macrobenthic community structure from one

dominated by EPT (Ephmeroptera, Plecoptera, Trichoptera)

taxa to another dominated by burrowing organisms (e.g.

Nuttal, 1972; Soluk, 1985; Wood and Armitage, 1997;

Chester and Norris, 2006). Our work suggests only a weak

concordance with this idea. In fact, although it is evident that

in May the most common and abundant taxa were members

of the Ephemeroptera and Trichoptera orders (Figure 3,

Table IX), and between August and November Diptera and

Oligochaeta reached appreciable percentages at M1 (Figure

3, Table IX), fine sediment-low oxygen tolerant Plecoptera

were the main component of the community close to the dam

in autumn. It seems that burrower organisms became a

dominant component just when sand quantities increased in

August, but quite surprisingly not when sand accumulation

further increased (Choy, 2004), a result that may be due to

the litter fall processes that influenced a dominance switch

from burrowers to shredders organisms.

CONCLUSION

The Mucone River below the Cecita Reservoir is a typical

metarhithron environment where pebbles and cobbles

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ABIOTIC AND BIOTIC GRADIENTS DOWNSTREAM A RIVER 115

prevail, the riverbed shows an high degree of microscale

and mesoscale spatial heterogeneity and autochthonous

primary production adds to allochthonous primary pro-

duction in channelling energy through macrobenthic

communities. The damming of the Mucone River, with

water restitution only a few kilometres downstream,

results in an interruption of ecological connectivity and

hydrological regimentation that is exacerbated during

the dry season. This produces a discontinuity in hydro-

geomorphological characteristics and trophic input sources

that in turn modifies the macroinvertebrate community

structure. The area close to the dam remains constantly

heterotrophic due to the narrowing of the river width and

fine sediment deposition that depress epibenthic micro-

algae growth, whereas when flow reactivates (after the

Cerreto tributary inflow) river width about doubles

and better irradiation enhances authocthonous primary

production. Lack of drift colonization below the dam

could be compensated by upstream larval migration

with the Cerreto tributary acting as a permanent source.

Density of niches, dominance and biodiversity levels

suffer due to strong seasonal sand deposition in the

area close to the dam but despite literature data such

geomorphological alteration promotes burrower taxa

colonization only temporally while the most successful

organisms were the CPOM consumer-fine sediment

tolerant Plecoptera that rely on high accumulation

of woody–leafy detritus favoured by the dam flow

regimentation effect.

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