Longitudinal variation in recolonization rates of macroinvertebrates along an upland river in south-eastern Australia

SUMMARY. 1. Recolonization rates of benthic invertebrates were estimated at five sites in the catchment of the Acheron River, in spring (October) and in summer (January), The sites ranged from those that experience short floods and high shear stress at the streambed (upstream sites) to those that experience prolonged floods and low shear stress (downstream sites). We hypothesized that these differences should affect recolonization rate.
2. In October, absolute rates of recolonization of taxa (number of taxa 0.05 m⁻² d⁻¹) onto 1-m² patches of substratum, which had been raked to remove fauna, did not vary between the three sites studied, nor did the relative rates of recolonization of taxa (absolute rate/mean number of taxa in control samples, which were taken from adjacent undisturbed patches of substratum). Absolute rates of recolonization of individuals (number of individuals 0.05 m⁻² d⁻¹) were proportional to the mean number of individuals in control samples; relative rates of recolonization of individuals (absolute rate/mean number of individuals in control samples) did not vary between sites.
3. In January, absolute rates of recolonization either of taxa or individuals were positively correlated with the mean densities of taxa or individuals in control samples; relative rates did not vary between the four sites studied.
4. We conclude that the benthic invertebrate communities at the various sites do not adapt to variations in flooding regime by altering relative recolonization rates. Absolute recolonization rates are directly proportional to the prevailing number of taxa or individuals at a site.     

Denitrification in river sediments: relationship between process rate and properties of water and sediment

1. A survey was made of denitrification and nitrous oxide (N₂O) production in river sediments at fifty sites in north‐east England during one season in order to investigate the relationship between rates and environmental factors likely to influence these processes. The sites were chosen to represent a wide range of physical and chemical conditions. Denitrification rate and N₂O production were measured within 5 h of sampling using the slurry acetylene blockage technique.
2. Denitrification rate ranged from less than 0.005–260 nmol N g^–1 DW h^–1, tending to increase in a downstream direction. N₂O production ranged from negative values (net consumption) to 13 nmol N₂O‐N g^–1 DW h^–1 and accounted for 0–115% of the N gases produced.
3. Denitrification rate and N₂O concentration in the sediment were correlated positively with nitrate concentration in the water column, water content of the sediment and percentage of fine (< 100 μm) particles in the sediment.
4. The variation in denitrification rate was satisfactorily explained (64% total variance) by a model employing measurements of water nitrate and water content of sediments. No simple or multiple relationship was found for N₂O production.     

Concentrations and annual loading of dissolved organic matter in a small moorland stream

SUMMARY. 1. Dissolved organic matter (DOM) was measured at 8h intervals over a 1 year period in a stream draining 51 ha of moorland with peaty soils.
2. DOM concentrations increased with increasing stream discharge from low flow values of 0–3 mg 1⁻¹ to maximum values of 30 mg 1⁻¹. There were also seasonal differences of up to 13mgl⁻¹ between August (maximum) and February, and differences of about 2.5 mg l⁻¹ between rising and falling stage samples.
3. Seasonal variation was closely related to mean temperature.
4. Total loss over the year was 168 kg ha⁻¹ DOM (84 kg ha⁻¹ C), larger than previous estimates for upland sites.     

Sediment microbial respiration in a synoptic survey of mid‐Atlantic region streams

1. The rate of microbial respiration on fine‐grained stream sediments was measured at 196 first‐ to third‐order sites in the mid‐Atlantic region of the United States.
2. Sample collection took place between April and July in 1993, 1994 and 1995.
3. Study streams were randomly selected from the United States Environmental Protection Agency's (USEPA) River Reach File (RF3) using the sample design developed by USEPAs Environmental Monitoring and Assessment Programme (EMAP).
4. Respiration rate ranged from 0 to 0.622 g O ₂ g^–1 ash‐free dry mass (AFDM) h^–1, and was significantly correlated with stream temperature, water chemistry and physical habitat.
5. Respiration rate was significantly higher in streams from the Chesapeake drainage area compared to those from the Ohio drainage area, and in streams from the Northern Appalachian Plateau and Uplands and Central Appalachian Valleys ecoregions compared with streams from the Blue Ridge and Central Appalachian Plateau ecoregions.
6. Respiration was not significantly different among stream orders or between years.     

Ammonium and phosphate regenerationby the zooplankton of an Amazon floodplain lake

SUMMARY. 1. Regeneration of ammonium and phosphate by macro-zooplankton (Cladocera. adult copepods. and copepodites) was measured in Lake Calado. an Amazon floodplain lake, Macrozooplanktonabundances ranged between 1×10⁴ and 3×10⁵ individuals m⁻².
2. Phosphate regeneration ranged from 0.2 to 1.3 μ mol PO₄ m⁻² b⁻¹at station 1. located 2 km from the Solimoes River, and from 1.6 to8.3 μ mol PO₄ m⁻² h ⁻¹ at station 3, located 7 km from the SolimoesRiver. Ammonium regeneration at stations 1 and 3 ranged from 1.7 to11.9 and from 13.4 to 77.2 μ mol NH₄ m⁻² h⁻¹. respectively.
3. Zooplankton regenerated ammonium and phosphate at similarrates during rising and falling waier. Regeneration by macrozooplankton was low compared to other tropical lakes and compared to microbesand microzooplankton in Lake Calado.     

Meteorological influences on algal bloom potential in a nutrient-rich blackwater river

1. The effect of variability in rainfall on the potential for algal blooms was examined for the St Johns River in northeast Florida. Water chemistry and phytoplankton data were collected at selected sites monthly from 1993 through 2003. Information on rainfall and estimates of water turnover rates were used in the analyses of trends in phytoplankton biomass.
2. Major trends in rainfall and runoff within the lower St Johns River catchment over the 10-year study period were marked by both significant drought and flood periods. Autumn and winter rainfall patterns were strongly correlated with the range of Pacific sea surface temperature anomalies associated with El Niño events and La Niña periods. The effect of these major shifts in rainfall was evident in the strong relationship to replacement rates for water within the lower St Johns River.
3. The eutrophic status of the river was reflected in the high concentrations of nitrogen and phosphorus observed at all sampling sites, with total nitrogen concentrations up to 3100  μ g L⁻¹ and total phosphorus concentrations up to 180  μ g L⁻¹.
4. While it is clear that the high phytoplankton biomass and frequent blooms that characterize the freshwater portions of the lower St Johns River are fundamentally based on nutrient status, the expression of that potential was strongly correlated to water replacement rates, as revealed by the inverse relationship between phytoplankton biovolume increase and water turnover rate, with an R ² of 0.80 for the major bloom season. The sensitivity of algal blooms to rainfall patterns over the 10-year study period suggest that longer-term temporal and spatial shifts in rainfall, such as multi-decadal cycles and the global-warming phenomenon, will also influence the frequency and intensity of algal blooms.     

The energetic importance of terrestrial arthropod inputs to three warm-water streams

1. Inputs of terrestrial arthropods (number and mass m^–2 d^–1) from riparian corridors to three streams representing different orders were highly variable among seasons and sites, with significantly greater ( P < 0.05) inputs at the headwater stream during summer months, compared with other sites and seasons.
2. No significant differences in estimates of stream retention of terrestrial arthropods (number and mass m^–2 d^–1) were observed among sites; however, retention of terrestrial arthropods at all sites was significantly greater during summer months, compared with other periods.
3. The gravimetric proportion of terrestrial arthropods present in the stomachs of redbreast sunfish ( Lepomis auritus ) and bluegill ( L. macrochirus ) was equivalent among sites. However, estimates of the dietary importance of terrestrial arthropods at all study sites were significantly greater in the summer, compared with other seasons.
4. Estimates of the potential annual energetic contribution (kJ m^–2 d^–1) of terrestrial arthropod inputs to the stream system were comparable with published rates of total annual production of aquatic macroinvertebrates in other Virginia headwater streams.
5. Results of this study supported the hypothesis that terrestrial arthropods represented an important energetic subsidy to stream fish during periods of low aquatic macroinvertebrate availability, and suggest that this component of allochthonous input is a potentially significant, but poorly understood energetic linkage between riparian landscapes and stream ecosystems.     

Population dynamics and production of Sialis lutaria L. (Megaloptera) in the Danish River Suså

SUMMARY. 1. Populations of Stalls lutaria L. were sampled quantitatively at about monthly intervals during 3 years at two localities in the macrophyte rich River Suså, Denmark.
2. The life cycle was univoltine. The larvae hatched in June-July, and the initial S. lutaria population densities varied between 10 and 370 ind. m⁻². These differences were probably due to extreme variations in stream discharge during the period of recruitment, high velocities preventing the small swimming larvae from reaching the sediment.
3. The S. lutaria rate of elimination varied between 0.11 and 1.47% d⁻¹at the two localities. The high rate of elimination was possibly due to fish predation.
4. The growth rates varied between 0.54 and 15% d⁻¹. Growth rates differed between localities and years.
5. Numbers of potential prey organisms were not higher in sample units with S. lutaria than in sample units without S. lutaria . Numbers of leeches, which were potential competitors, did not differ significantly in sample units with and without S. lutaria .
6. Production of S. lutaria varied between 0.16 and 2.49 g ash free dry weight m⁻² y⁻¹, and the P/ ratios varied between 3.0 and 7.3 y⁻¹. The P/ ratios increased significantly with increasing rate of elimination.     

Breakdown of tussock grass in streams along a gradient of agricultural development in New Zealand

Summary 1. We measured the breakdown rate of tussock grass in 12 New Zealand streams in catchments that provided a gradient of agricultural development. We also examined the microbial and invertebrate communities associated with decomposing tussock litter.
2. Pristine streams in the study had low concentrations of dissolved inorganic nitrogen (<10  μ g L⁻¹) and dissolved reactive phosphate (<3  μ g L⁻¹), whereas streams in the most developed catchments had high concentrations of nitrate (>2500  μ g L⁻¹) and phosphate (35  μ g L⁻¹), as well as greater amounts of suspended sediment and fine sediment covering the streambed.
3. Breakdown rate and microbial respiration were significantly related across the sites, and both were positively related to concentrations of nitrate and phosphate. Fungal biomass, measured as ergosterol, was positively related to microbial respiration and was also higher at sites with higher concentrations of nutrients. Total and shredding invertebrates were most abundant at the sites with high nutrient concentrations, but abundance of shredding invertebrates was not significantly related to breakdown rate. Amphipods were the most common shredding invertebrate at most sites, but probably did not contribute greatly to high rates of breakdown in streams in agricultural catchments.
4. With the exception of one site, nutrients from agricultural development appeared to have larger positive effects on litter breakdown than negative effects from sedimentation. Litter breakdown can serve as a functional measure of ecosystem health in streams, but caution should be exercised when a stress, such as land use, can have both positive (nutrients) and negative (sedimentation) effects.     

Causes of episodic acidification in Alpine streams

SUMMARY 1. Despite their global importance as mountain landscapes, the effect of acid deposition on running waters in the Alps is still incompletely described. The acid–base status of 30 clearwater streams in Canton Ticino (Switzerland) was therefore assessed at low and high flow across a south/north gradient of acid deposition in 2000.
2. At low flow, no stream was acidic, alkalinity being ≥29 μeq L⁻¹ and pH ≥6.4. However, NO₃^– was present in streamwater at these flows in concentrations that suggested anthropogenic enrichment, and its concentration correlated with spatial patterns of N deposition from the atmosphere.
3. Severe loss of alkalinity occurred in most streams at high flow during snowmelt (spring) or rainstorms (spring and autumn). Autumn episodes were because of dilution of streamwater alkalinity by rainwater. By contrast, spring episodes involved dilution and NO₃^– titration, the increase in nitrate being correlated with patterns of N deposition. SO₄^2– declined during most episodes.
4. High NO₃^– leaching at low flow suggests that catchment soils in Canton Ticino are approaching saturation in N. These data are among the first to illustrate that NO₃^– can drive episodic acidification in Europe, paralleling locations in north-eastern United States.     

The energetic importance of terrestrial arthropod inputs to three warm-water streams

1. Inputs of terrestrial arthropods (number and mass m^–2 d^–1) from riparian corridors to three streams representing different orders were highly variable among seasons and sites, with significantly greater ( P < 0.05) inputs at the headwater stream during summer months, compared with other sites and seasons.
2. No significant differences in estimates of stream retention of terrestrial arthropods (number and mass m^–2 d^–1) were observed among sites; however, retention of terrestrial arthropods at all sites was significantly greater during summer months, compared with other periods.
3. The gravimetric proportion of terrestrial arthropods present in the stomachs of redbreast sunfish ( Lepomis auritus ) and bluegill ( L. macrochirus ) was equivalent among sites. However, estimates of the dietary importance of terrestrial arthropods at all study sites were significantly greater in the summer, compared with other seasons.
4. Estimates of the potential annual energetic contribution (kJ m^–2 d^–1) of terrestrial arthropod inputs to the stream system were comparable with published rates of total annual production of aquatic macroinvertebrates in other Virginia headwater streams.
5. Results of this study supported the hypothesis that terrestrial arthropods represented an important energetic subsidy to stream fish during periods of low aquatic macroinvertebrate availability, and suggest that this component of allochthonous input is a potentially significant, but poorly understood energetic linkage between riparian landscapes and stream ecosystems.     

The seasonal biomass and productivity of the submerged macrophytes in a polluted Wisconsin stream

SUMMARY 1. We measured biomass and light/dark bottle productivity of macrophytes in a Wisconsin stream throughout one growing season. Except for a brief period in early spring when a Cladophora glomerata -filamentous algal community was dominant, Potamogeton pectinatus was the dominant macrophyte species in Badfish Creek.
2. Maximum community biomass was 710 g DW m⁻², with a maximum above ground biomass of 620 g DW m⁻² and a maximum below ground biomass of 120 g DW m⁻². Annual productivity was estimated at 1435 g DW m⁻² year⁻¹, with a calculated P/B of 2.01.
3. In situ net production averaged 2.83g C g AFDW⁻¹ h⁻¹ Net positive carbon gain by the P. pectinatus community occurred when water temperatures were above 15°C, and daylength at least 12h. This is correlated to the onset of tuber germination in spring, and the point of maximal biomass decline in autumn.     

Dissolved organic carbon concentrations and fluxes along the Moisie River, Quebec

SUMMARY. 1. The main stream and tributaries of a 145 km reach of the Moisie River, Quebec, were examined for temperature, conductivity, pH, dissolved organic carbon (DOC),%DOC>100,000 nominal molecular weight (NMW), optical density (OD₃₅₀), and the ratio of OD₄₀₀ to OD₆₀₀ (E4:E6).
2. Dissolved organic carbon concentrations correlated closely with OD₃₅₀ ( r ²=0.92, P <0.001). However,%DOC>100,000 NMW did not correlate with the E4:E6 ratio.
3. Except for a slight increase in%DOC> 100,000 NMW ( r ²=0.37, P <0.05), no change in any characteristic occurred down the length of the Moisie River, despite consistently higher levels of DOC in the tributaries.
4. Results suggest that high concentrations of DOC in tributary waters are rapidly removed within the main river channel. These results are discussed in terms of both biotic and abiotic models of in-strcam processing.     

Major ion chemistry of the lower Boro River, Okavango Delta, Botswana

SUMMARY. 1. The composition of surface waters of the Boro River, Okavango Delta, Botswana, was determined on five occasions during 1989–1990. The waters could be characterized as caicium—sodium—bicarbonate, with moderate alkalinity, and moderate to high amounts of silica. Mean values of the major ions, in mg1-⁻¹, were: Ca²⁺ 4.8, Mg²⁺ 1.3, Na⁺ 3.9, K⁺ 2.7, HCO₃⁻ 27, Cl⁻ 1.0 and SiO₂ 38; pH c. 7.
2. The relative ionic composition of the waters changed gradually from the inlet in Seronga to the outlet at Boro/Thamalakane junction. There was a gradient of increasing concentrations of solutes resulting from the evaporative concentration of the waters in this semi-arid region with an almost permanent water deficit, and the total dissolved solutes increased from c. 30 to 95 mg 1-⁻¹
3. There were seasonal differences in solute concentrations, connected with the rainfall pattern and climatic cycle and an ill-defined relation with discharge. The chemical spectrum of the Boro, and the freshness of its waters, can be attributed to the major influence of precipitation within the basin and selective removal of solutes.
4. Chemical equilibrium models indicate that amorphous silica and sepiolite are likely to precipitate from the Boro waters. Carbonate and silicate systems are responsible for the selective removal of solutes in the swamps, islands, or flood plains, as proposed by others in recent studies, but not in the Boro River waters.     

Respiration rate in maize roots is related to concentration of reduced nitrogen and proliferation of lateral roots

The relationship between specific rate of respiration (respiration rate per unit root dry weight) and concentration of reduced nitrogen was examined for maize ( Zea mays L.) roots. Plants with 2 primary nodal root axes were grown for 8 days in a split-root hydroponic system in which NO-₃ was supplied to both axes at 1.0 mol m⁻³, to one axis at 1.0 mol m⁻³ and the other axis at 0.0 mol m⁻³ or to both axes at 0.0 mol m⁻³ Respiration rates and root characteristics were measured at 2-day intervals. Specific rate of respiration was positively correlated in a nonlinear relationship with concentration of reduced nitrogen. The lowest specific rates of respiration occurred when neither axis received exogenous NO⁻³ and the concentration of reduced nitrogen in the axes was less than 9 mg g⁻¹. The greatest rates occurred in axes that were actively absorbing NO⁻³ and contained more than 35 mg g⁻¹ of reduced nitrogen. At 23 mg g⁻¹ of reduced nitrogen, below which initiation of lateral branches was decreased by 30–50%. specific rate of respiration was 17% greater for roots actively absorbing NO⁻³ than for roots not absorbing NO⁻³ Increases in specific rate of respiration associated with concentrations of reduced nitrogen greater than 23 mg g⁻¹ were concluded to be attributable primarily to proliferation of lateral branches.     

The relationships among three habitat scales and stream benthic invertebrate community structure

1. The relationships between three habitat scales and lotic invertebrate species composition were investigated for the 15 540 km² Yakima River basin in south-central Washington, U.S.A.
2. The three spatial scales were sample (the sampled riffle), reach (a length of ten–twenty stream widths) and segment (a length of stream of nearly uniform slope and valley form having no change in stream order).
3. Physical variables were highly correlated between scales and expressed a relationship between altitude, basin form and small-scale physical structure.
4. Multiple discriminant function analyses indicated that segment- and reach-scale variables discriminated among species-defined groups better than sample-scale variables.
5. Species composition varied along a complex altitudinal gradient of changing basin form and resultant land use.
6. There was no clear relationship between species richness and altitude on a site basis. However, when viewed at the basin scale, maximum richness was observed at the transition between montane and valley sites.     

The relationships among three habitat scales and stream benthic invertebrate community structure

1. The relationships between three habitat scales and lotic invertebrate species composition were investigated for the 15 540 km² Yakima River basin in south-central Washington, U.S.A.
2. The three spatial scales were sample (the sampled riffle), reach (a length of ten–twenty stream widths) and segment (a length of stream of nearly uniform slope and valley form having no change in stream order).
3. Physical variables were highly correlated between scales and expressed a relationship between altitude, basin form and small-scale physical structure.
4. Multiple discriminant function analyses indicated that segment- and reach-scale variables discriminated among species-defined groups better than sample-scale variables.
5. Species composition varied along a complex altitudinal gradient of changing basin form and resultant land use.
6. There was no clear relationship between species richness and altitude on a site basis. However, when viewed at the basin scale, maximum richness was observed at the transition between montane and valley sites.     

Modelling black fly production dynamics in blackwater streams

SUMMARY. 1. Two predictive models were employed along with intensive field sampling to estimate production of black flies ( Simulium spp.) on snags (submerged wood) in three blackwater streams on the Georgia Coastal Plain of the southeastern U.S.A. One model predicts daily growth rate from temperature and hydrograph pattern; the other predicts habitat abundance (of snags) from river height.
2. In the sixth order Ogeechee River, annual production was twice as high in 1982 (7.1 g dry mass [=DM] m⁻² of snag surface) as in 1983 (3.6 g DM m⁻²). When converted to production per m² of river bottom, values were 35–40% of the snag surface estimates. Annual production was much lower in fourth order Black Creek (1982, 1.3 g DM m⁻² of snag surface) and much higher in the sixth order Satilla River (1975, 15.6–40.0 g DM m⁻²).
3. There was a distinct bimodal pattern of black fly production in the Ogeechee River in both years, with peaks occurring in winter and summer. Similar bimodal patterns of production were found in Black Creek and in the Satilla River. Although there appears to be an intrinsic component to the bimodal pattern, production peaks (growth rate and biomass) appear to be associated with initial stages of flooding.
4. Annual production/biomass ratios (37–85) are the highest reported for black fly populations. The variation of annual P/B ratios among sites was more strongly dependent on the temporal distribution of standing stock biomass than on differences in growth rates. Variation in production among sites appears to be due to differences in current velocity, hydro-graph variability, and abundance of coexisting consumers.     

Predicting zebra mussel fouling on native mussels from physicochemical variables

1. Predictive models of impact are needed for the risk assessment of invasive species. One such species is the Eurasian zebra mussel ( Dreissena polymorpha ), a fouling bivalve that overgrows and kills native mussels (Unionidae) in many North American lakes and rivers. The level of mortality in a native mussel population increases with the fouling intensity – i.e. the mean number of zebra mussels attached to each native mussel.
2. We conducted a multi-site survey within the St Lawrence and Richelieu rivers (Quebec, Canada) to determine whether zebra mussel fouling intensity can be predicted from environmental variables. We found fouling intensity to be positively correlated with calcium concentration [Ca²⁺] and negatively correlated with sediment size, but not affected by local macrophyte cover.
3. A multiple regression model that includes calcium concentration and sediment size explains 86% of variation in fouling intensity across all sites.
4. Analysis of data from invaded sites in North America and Europe revealed a nonlinear relationship in which fouling intensity increases with calcium concentration up to an asymptotic threshold of 24 mg L⁻¹ Ca²⁺.
5. Our results suggest that the community-level impacts of zebra mussels are mediated by abiotic environmental variables and gradients in these variables may provide local habitat refugia for native mussels.     

Metabolism of a sub-tropical low gradient black water river

SUMMARY. 1. Single-station diel oxygen curves were used to monitor the oxygen metabolism of the Ogeechee River, a sixth-order blackwater river in the Coastal Plain of southeastern U.S.A., over a period of 4 years. Ecosystem production ( P) and respiration (R) were estimated, and P/R ratios calculated to determine the extent of autotrophy characteristic of this type of river. The potential error in oxygen metabolism caused by photo-oxidation of dissolved organic carbon (DOC) in the water was measured and found to be minor.
2. Rates of ecosystem primary production measured were intermediate compared to other rivers, ranging from 0.49 to 13.99g O₂m⁻² day ^−1.Primary production rates were highest during the summer when water levels were low. Regression analysis indicated that water depth and light absorption by DOM were significant predictors of primary production in this river. Incident light intensities were not significantly correlated with production rate.
3. Respiration rates were unusually high, varying between 3.70 and 11.5 g O₂ m⁻² day ^{− 1}. System respiration also varied seasonally, but less than primary production. Rates were slightly higher in spring and summer.
4. With one exception, P/R ratios were considerably lower than l throughout the study period, indicating that the Ogeechee River was highly heterotrophic. PIR ratios ranged from 0.09 to 1.3, and averaged 0.25.
5. A carbon budget calculated for this river showed floodplain inputs were 7 times autochthonous production. Organic carbon turnover length was 690 km, considerably longer than has been reported for lower-order rivers.