Understanding Ecological Responses to Hydrologic Alteration in Streams and Rivers IV Posters
Presiding: M Gurtz, U.S. Geological Survey; M Freeman, U.S. Geological Survey
NB33G-01 1330h
The downstream effect of hydropower release in an Alpine glacial stream
Hydroelectric power production is highly important in Alpine areas and recent research has highlighted the ecological problems caused on river ecosystems, changing public opinion from a general approval of hydropower as "renewable and environmentally clean" to a more critical position. Most research has focused on the effects of water abstraction and dams, and less on water release in the channel from power plants. The aim of our work is to contribute to this scientific debate. Here we present results from a study on the Noce, a stream dominated by glacial run-off in the central-eastern Italian Alps. Water is stored in a reservoir at 2600 m a.s.l., and released through turbines at 1900 m a.s.l. It then is mixed with water from another watershed and released again in the Noce through turbines at 1300 m a.s.l. Temperature was recorded at hourly intervals above and below the last power plant. Conductivity, turbidity, oxygen and various chemical parameters were recorded hourly over 12 h on different occasions. The structure of the zoobenthic community was analysed above and below the lower release. Results indicate major hydro-peaking effects on the physical proprieties of the stream and on the zoobenthic community.
NB33G-02 1330h
Is the Seasonal Water Flow a Regulator of Zoobenthos Movements in the Colonization Process of a Stream Sandy Substrate?
This work aimed to evaluate the importance of routes of colonization of sandy substrate in an urban Atlantic forest stream (Cantareira State Park, São Paulo, Brazil), during low and high flow seasonal conditions. Natural sediment of the stream was boiled, filled in perforated plastic baskets and implanted in the stream bed. The baskets were modified in two ways, one to restrict upward subsurface colonization and other to restrict water route of colonization (aerial, drift and downstream and upstream movements). Baskets without restriction were implanted as control. Three sampling units of each basket were exposed for 7, 14, 21 and 28 days, during three sampling periods of low and high flow seasonal conditions respectively. In both seasons, zoobenthos densities and family richness were frequently higher in water route colonized baskets than in subsurface route colonized baskets. However, benthic families' persistence in subsurface samples increased conspicuously in the end of rainy season, in spite of no significative correlation between this community parameter and any water movement variable has been founded. These results indicates subsurface route as more important in the process of colonization in dry season. Just Orthocladiinae showed preference on water route and Tanytarsini on interstitial route.
NB33G-03 1330h
Long Wall Mining Subsidence and Fluvial Stream Changes: an Ecological Perspective
Long wall mining is a high efficiency underground coal extraction technique that removes large panels of coal and causes immediate subsidence of the overburden. Surface subsidence may vary between 0.3 meters and 2 meters depending on the depth of the coal seam. Fractures in the overburden allow perched water tables to drain to greater depths and dries up their associated springs. Base flow in headwater streams is often eliminated. Subsidence also changes the physical characteristics of streams. Typical riffle pool sequences are replaced with long pools and glides. Benthic invertebrate and fish community assemblages reflect the physical habitat changes. EPT invertebrate taxa are replaced with Odonates and Diptera larvae associated with glide/pool habitat. Fish community diversity is negatively impacted. Diverse riffle dwelling assemblages are replaced and dominated by increasingly homogenous pool dwelling fish communities. Stream subsidence effectively increases the stream order without increasing its size or flow regime.
NB33G-04 1330h
Effects of Current Velocity, Particle Size, and Substrate Heterogeneity on Crayfish (Orconectes propinquus) Activity
The use of flow refugia (e.g., substrate) by lotic invertebrates often increases their likelihood of survival during flood events. Movement to potential refugia becomes risky as velocities increase, and the range of velocities that benthic invertebrates can withstand is variable. In this study, activity time and slip velocities of small [carapace length (CL)=10-20 mm] and large (CL=20-30 mm) Orconectes propinquus were measured in an artificial flume across ranges of current velocity and substrate heterogeneity. Particle sizes included small pebbles (16-32 mm), large pebbles (32-64 mm), and small cobble (64-128 mm). Water velocity was increased by 0.1 m/s increments from 0.1-1.5 m/s at 5-minute intervals or until the crayfish was dislodged from the substrate. As current velocity increased, the probability of slipping increased for all crayfish. Regardless of the degree of substrate heterogeneity, small crayfish held their position at higher velocities than large crayfish and were also less active. Slip rates were generally lower for both sizes as substrate heterogeneity increased. Essentially, the availability and probability of finding refugia increased with increased habitat heterogeneity and allowed crayfish to avoid being swept into the drift.
NB33G-05 1330h
Short Term Effects of Dam Removal Upon Trichopteran Communities
To determine the impact of dam removals upon in-stream insect communities, we monitored the removal of two small dams on Boulder Creek, a second order trout stream in Wisconsin. We used six Trichopteran genera (Brachycentrus, Glossosoma, Ceratopsyche, Lepidostoma, Pycnopsche, and Dolophilodes) as indicators of the overall effects of these dam removals. Benthic samples were collected upstream and downstream of the dams before and after the removals. Prior to removal, densities decreased gradually in the upstream and downstream reaches. Immediately after removal, there was an 83% decrease in total downstream density compared to an upstream decrease of only 34%. In the six weeks following removal, the downstream density increased by 255%, approaching pre-removal densities, while the upstream density showed no major change. The decrease in population densities downstream was most likely due to scouring and burial by reservoir sediments during the removal. Rapid downstream recovery following removal was likely due to recolonization from upstream populations. Overall, effects of the removals were extremely brief (6 weeks or less), demonstrating that the removal of these dams was not a major disturbance to the Trichopteran community.
NB33G-06 1330h
The influence of catchment land use on hydrograph dynamics and implications for stream biological assemblages
Catchment land use impacts the rise and fall dynamic of hydrographs, and may also help explain variation in biological assemblages known to be sensitive to flow regime. We collected continuous stream depth records for the 2002 water year (5 min. intervals) from eight streams draining catchments ranging in size from 17 to 58 km2. Correspondent data for stream biological communities was collected on an annual basis from 1999 to 2002. High-resolution aerial photos from 2002 showed that land use over the eight catchments fell over a gradient in the extent of unvegetated, barren land, which ranged from 2 to 14 percent. Storm hydrographs were analyzed for duration and rate constants, and for both rising and falling limbs. Although we expected moderate urbanization in certain catchments to affect rise rates, we were surprised to find that no particlar type or percentage land use correlated with characteristics of the rising limb. An increased proportion of barren land, however, significantly decreased the duration of the falling limb relaxation curve and its mass. The degree to which the unprotected barren areas emulate impervious surface may have increased the proportion of precipitation converted to runoff during storm events, limiting the potential for longer term recharge. This change in hydrology affected habitat availability and quality, which we furthermore discuss in the context of effects on stream biological assemblages. 1
NB33G-07 1330h
Preliminary analysis of bed and suspended sediment transport in a protected watershed, and the effect on native mussel populations
Sediment budgets in river networks are notoriously difficult to construct, but can be important for quantifying short and long-term changes to fluvial environments. Adequate sediment supply is critical for in channel, bar, and near-shore ecosystems; too much or too little sediment can be a detriment to biota, including mussels and host fish. Hornbach and others (see http://www.macalester.edu/~hornbach/St.Croix/index.html) have been collecting bed sediment at various locations along the St. Croix River since 1990 in an effort to understand controls on mussel population and diversity. These data, along with suspended sediment data collected by other agencies (e.g., Triplett and others, 2003; Metropolitan Council, 2004), can be used to examine trends in sediment transport and/or sediment delivery to the river over time. We continued the collection of bed sediment in conjunction with mussel quadrat surveying in summer 2004, and initiated sampling of suspended sediment at various locations along the river. We developed rating curves (relating suspended sediment concentration and mean daily water discharge) for several locations along the St. Croix River, and compared these to historical data. In addition, we examined trends in bed sediment grain size over the last decade. Analysis suggests that while bed sediment grain size is relatively unchanged in most of the study areas, there has been a fining trend in the region below the St. Croix Falls dam. This corresponds with a decrease in the juvenile population of the winged mapleleaf mussel, a federally-endangered species found almost exclusively in this part of the St. Croix (Hornbach, 2005). Future research will address fluvial dynamics and sources of fine sediment in this region. Suspended sediment data are more limited, but suggest transport dynamics may have changed over the last half century.
NB33G-08 1330h
An Index of Longitudinal Hydrologic Connectivity to Evaluate Effects of Water Abstraction on Streams Dominated by Migratory Shrimps
Massive water withdrawals from streams draining the Caribbean National Forest (CNF), Puerto Rico, are threatening their biotic integrity. Migratory tropical shrimps are ideal indicator species to measure water withdrawal effects on riverine connectivity and biointegrity because: (1) their migratory range encompasses the stream network from estuaries to headwater streams; (2) they represent greater than 90% of biomass in streams draining the CNF; and (3) they facilitate important in-stream ecological processes. We developed an index to evaluate individual and cumulative effects of water intakes on each stage of the shrimp's life-cycle. Effect of water withdrawal on longitudinal connectivity was evaluated by combining effects of water withdrawal on larval and juvenile shrimps. Larvae require downstream transport to the estuary for advancement to the next life-stage, and juveniles similarly require access to headwater streams. Therefore, these two life-stages represent the bi-directional connectivity of streams from headwaters to estuaries. Seventeen water intakes were evaluated in and around the CNF. Larger intakes cause a greater decrease in connectivity than smaller intakes; however, several small, high elevation intakes had very low connectivity. Also, intakes with alternative designs, such as a French drain, have reduced effects on connectivity.
NB33G-09 1330h
The Effect of Contrasting Drought Disturbance Regimes on Autrophic Communities
Experimental channels (4 blocks x 3 channels; 12.5 m long x 0.3 m wide) fed by stream water were used to assess the effects of contrasting dewatering regimes on autrophic communities over a 21 month period from May 2000 to April 2002. Communities in undisturbed control channels were compared with those subject to different episodic dewatering (5-day duration) regimes. Epilithic biofilms in each channel were sampled quantitatively (6 stones, upper surface area x-y cm2) at monthly endpoints, enabling comparison of disturbed communities with contemporaneous controls. Aliquots were drawn from samples to determine biofilm ash-free dry mass, chlorophyll content and auotrophs were identified to species. Frequent droughts were found to decrease the richness and abundance of core autotrophic taxa and promoted a shift in dominance from eukaryotic green algae to cyanobacteria.
NB33G-10 1330h
When the Well Runs Dry: Ecological Consequences of Dewatering Rivers
Disturbances related to river discharge are thought to define the physical template that structures biological communities and selects for effective life history strategies. Through managing river discharge to support agricultural production in arid and semi-arid landscapes, the timing, frequency, magnitude, and duration of low flow events has been altered. Despite the ubiquitous nature of this management practice, we are currently unable to predict when low flow events impose a disturbance on lotic ecosystems or the spatiotemporal extent of biotic responses. This poster outlines a study that examines gradients in water withdrawal intensity to: 1. Determine if macroinvertebrate communities and environmental variables exhibit threshold or proportional responses to channel dewatering; 2. Characterize spatiotemporal response and recovery patterns of macroinvertebrates to low flow disturbances; 3. Compare life history traits, growth, and developmental rates for invertebrates inhabiting different flow regimes. Preliminary results show macroinvertebrate community structure changing at greater spatial and temporal rates as compared to reference conditions when discharge is reduced by 75 percent or more. The characterization of macroinvertebrate response and recovery patterns to low flow events will help develop innovative strategies that allow agricultural water use, while mitigating structural and functional impacts on lotic systems.
NB33G-11 1330h
Stream Habitat Modeling to Support Water Management Decisions for the North Fork Shenandoah River, Virginia
The Shenandoah River and its tributaries, the North Fork and South Fork, represent an excellent model of a multiple use river. Due to documented fish kills, frequent low flow events, and proximity to the Washington D.C. metropolitan area, there is growing concern regarding the sustainability of this natural resource. In 1999, a four-year IFIM (Instream Flow Incremental Methodology) study was initiated to evaluate the response of hydraulics and fish habitat to low flow conditions in the North Fork Shenandoah River (NFSR) basin. Habitat suitability criteria were developed onsite for guilds of riffle, fast generalist, pool-run, and pool-cover fishes. Habitat responses to stream flows were quantified for these habitat guilds and habitat conditions conducive to nuisance algal blooms. In addition, we compared usable habitat conditions under baseline and alternative hydrologic time series corresponding to water use restrictions. Model results were used to identify aquatic conservation flows and establish a stepwise process for implementing aquatic conservation flow management in the NFSR basin. This process will facilitate the adoption of water use conservation measures at appropriate times during future extreme droughts.
NB33G-12 1330h
Linking Shifts in Community and Trophic Structure to Altered Streamflow Regime
Recent studies discuss the coupling of lotic organisms to stream flow patterns and how human induced hydrographic alterations can disrupt these relationships. The objective of this study is to develop correlations between specific deviation in the natural streamflow patterns with shifts in trophic and community structure in low order alpine streams in eastern California. To isolate the impact of altered flow regime on periphyton and benthic macroinvertebrate communities, relatively undisturbed regulated and unregulated stream reach pairings were selected based on similar geographic and geomorphic characteristics. Although analyses of abiotic parameters show little difference between stream reach pairings, preliminary analyses of biological data show a reduction in the BMI community diversity (H), a decrease in the scraper abundance, and an increase in Chlorophyll A in regulated reaches. Initial investigations of stream hydrographs show an increase in summer and winter flows and a decrease in spring high flows in regulated streams. Future investigations will analyze fish communities, temperature variability, and water quality parameters with the goal of determining if specific shifts in community and trophic structure can be correlated to specific deviations in the natural hydrograph, and if so, which components contribute the most to structuring these communities.
NB33G-13 1330h
A Test of the Serial Discontinuity Concept Using Pre- and Post-Impoundment Data: do Ecosystems Recover?
Many rivers are influenced by human-made impoundments that alter natural habitat. Changes in habitat hold potential consequences for biotic community structure and ecosystem function. The serial discontinuity concept (SDC), however, predicts that riverine process and function will recover downstream from an impoundment via tributary inputs. Unfortunately, rivers rarely exist in the context assumed by the SDC. Often, watersheds include multiple impoundments and other flow-altering structures. We present preliminary data and future research goals to investigate the changes in riverine habitat and benthic community structure before and after impoundment over 400 km of the Oldman River, southern Alberta, Canada. Habitat characteristics and benthic invertebrate abundance and community structure prior to dam construction were tested against post-impoundment data. Results indicate that 15 years after impoundment, flow and sediment regimes have not recovered. There is a significant decline in discharge during high flow periods below the dam and a pattern of decreased sediment transport and increased retention below the dam. Initial results have serious implications to benthic invertebrates, many of which require cobble substrates for colonization. The preliminary results on habitat alteration below the Oldman Dam do not support the predictions of the SDC.
NB33G-14 1330h
Local vs. Regional Effects on Fish Diversity as Mediated by Streamflow Disturbance Regime
The interplay of local and regional processes on fish diversity is poorly understood, especially related to patterns of streamflow disturbance regime. Articulation of the relationship between flow disturbance patterns and river fishes across local to regional scales is critical for resolution of some of our most difficult conservation challenges. This analysis addresses the following questions: (1) How do patterns of flow disturbance regime array across the landscape at multiple scales? (2) How are patterns of fish diversity distributed across the same landscape? (3) How does the relationship between flow regime and fish diversity vary at different levels of spatial scale? My study area was the upper Missouri River Basin in Montana and the Dakotas. Streamflow disturbance was defined by metrics derived from U.S. Geological Survey streamflow data. Fish data were provided by the U.S. Environmental Protection Agency as part of the Environmental Monitoring and Assessment Program (EMAP). The relative influences of local and regional processes on fish diversity were quantified by additive partitioning of total diversity (gamma) into local (alpha) and regional (beta) components. Diversity components were evaluated in the context of the streamflow regime to determine the relative importance of different streamflow factors across the range of scale.
NB33G-15 1330h
Downstream Effects on Water Quality From Reservoir Drawdown in Southeast Idaho
During normal operations in agricultural water delivery, water levels in American Falls (Snake River) and Blackfoot (Blackfoot River) reservoirs decline in late summer and fall. When reservoir volumes reach certain low levels, water released downstream has increased suspended sediment concentrations. This sediment-laden water potentially impacts coldwater aquatic life and salmonid fisheries. To assess impacts to downstream water quality, we collected water quality data above and below the reservoirs. Turbidity below reservoirs was elevated over inflow background levels and was influenced primarily by reservoir level. Turbidity during these periods exceeded both instantaneous and 10 consecutive day average numeric criteria of 50 and 25 NTU, respectively. Downstream phosphorus and nitrogen were significantly elevated compared to upstream sites. Dissolved oxygen in Blackfoot River below Blackfoot reservoir did not meet cold water criteria of 6 mg/L numerous instances during the monitoring period. Our data suggests maintaining minimum reservoir pools would help meet water quality standards and maintain beneficial uses in downstream reaches of these rivers. Failure to maintain minimum reservoir levels in light of increasing demand and extended drought cycles will continue to negatively impact water quality and beneficial uses in these important river reaches.
NB33G-16 1330h
Community Resilience and Resistance in Regulated Rivers.
Across diverse ecosystems, environmental factors such as nutrient loading have been shown to induce changes in state and reduce ecosystem resilience. Riverine communities are under increasing pressures from nutrient loading and fragmentation and it is unknown how these pressures will affect community resistance and resilience. This study focuses on determining 1) if nutrient loading and regulation change the resilience and resistance of rivers to further disturbances (floods); and 2) how particular community features create resilience and resistance. Along nutrient and algal biomass gradients in regulated and unregulated reaches of the Saint John River, Canada, community resilience (system capacity to return to its original state post disturbance) is examined both temporally and spatially. Resistance (ability to resist change) is measured by the nutrient concentration at which a change in ecological state occurs. State includes both community structure (species abundance and diversity of benthic algae and invertebrates) and community function (photosynthesis to respiration ratio). To determine how community features create resilience, trophic decoupling and food web connectance are examined along nutrient and physical disturbance gradients by comparing food webs constructed from stable isotope and biomass information. Because decreased resilience is linked with state shifts, strategies for sustainable ecosystem management should focus on maintaining resilience.