Temporary Waters: Ecological Values, Policy, and Management II
Presiding: K Fritz, U.S. Environmental Protection Agency; B Johnson, U.S. Environmental Protection Agency
NB22B-01 10:30h
Hydrochemistry and Periphyton in the Perennial, Intermittent, and Ephemeral Selwyn River, South Island, New Zealand.
The Selwyn River flows from the Southern Alps across an alluvial plain to the South Island's east coast. The mainstem loses water to an unconfined aquifer for 40 river kms, then gains water from a confined aquifer for 20 kms. The presence and magnitude of flow at any point is controlled by upstream discharge and/or local groundwater level. Flow permanence ranges from 100% at the furthest upstream (run-off dominated) and downstream (groundwater-dominated) reaches to 10% in the central reach. Flow permanence also varies among small-scale habitats: backwaters and remnant channels have greater permanence than riffles and runs. In the gaining reach, conductivity and sodium, nitrate, and inorganic phosphorus concentrations are 2-7 times higher than in the losing reach. A subreach within the losing reach is dominated chemically by tributary inflows. Differences between gaining and losing reaches diminish when they are hydrologically-connected, but connection only occurs about 60 d/yr. Between-reach differences are primarily due to solute-enriched influent groundwater. Flow permanence is a poor predictor of water chemistry, in part because tributaries alter flow permanence and chemistry simultaneously. In contrast, periphyton biomass is closely related to flow permanence, suggesting that emersion in intermittent reaches limits periphyton growth more than nutrient availability.
NB22B-02 10:45h
Flow Permanence Controls Fish and Invertebrate Assemblages at Multiple Spatial Scales in a New Zealand Gravel Bed River
Intermittent flows are a natural feature of many alluvial plain rivers of New Zealand, however water abstraction and climatic variability can greatly affect both the duration and spatial extent in loss of surface flows. We have initiated a long-term study on the Selwyn River, Canterbury, with the aim of determining how interactions between natural flow variability and water abstraction control invertebrate and fish communities through variation in flow permanence. River discharge along the 40 km study section is simultaneously controlled by runoff from the foothills and groundwater levels along the plains, with permanence ranging from 100% at both the runoff dominated upper reaches and groundwater dominated lower reaches, to <10% in the middle reaches. During contiguous flow, invertebrate assemblages formed two distinct groups characterized by contrasting life histories: a univoltine/semivoltine group at the top and bottom of the river where flow permanence exceeds 80%, and a multivoltine group in the central reaches where flow permanence ranges from 10 to 75%. Distinctive fish assemblages characterized upper and lower portions of the river, possibly reflecting impairment of dispersal across intermittent middle reaches. Only relatively small numbers of fish dispersed into intermittent middle reaches, with the greatest fish densities at sites with >80% flow permanence. Results of our study indicate that changing flow permanence leads to spatial and temporal patchiness in habitat availability, with significant consequences for biodiversity and ecosystem function.
NB22B-03 11:00h
Factors Controlling Hydrologic Permanence of Headwater Streams
Headwater streams compose the majority of stream miles within most drainages. Interest in monitoring headwater streams is increasing because these streams are vital linkages between upland land use and downstream water bodies. However, traditional stream assessment tools are often unsuitable because many headwater streams are prone to natural drying. Our objective was to identify physical characteristics of headwater reaches that are indicative of hydrologic permanence, a critical first step in applying a stream assessment. We surveyed 61 reaches along 17 headwater streams (< 2.6 km2) across 4 forests in Indiana, Kentucky and Ohio. Reaches varied in hydrologic permanence over the 2-year study. Exploratory data analysis (CART and discriminant analysis) was used to identify physical parameters for classifying reaches by hydrologic permanence. Drainage area was a consistent parameter discriminating permanence categories and consistently separated ephemeral from perennial and intermittent reaches. Secondary parameters that distinguished intermittent from ephemeral and perennial reaches included bankfull width, maximum pool depth, and channel entrenchment. These factors represent basin and reach scales, suggesting that hydrologic permanence in stream networks should be investigated in a hierarchical context. Although this work was reviewed by EPA and approved for publication, it may not necessarily reflect official Agency policy.
NB22B-04 11:15h
Are Salamanders Useful Indicators of Hydrologic Permanence in Headwater Streams?
Regulatory agencies need appropriate indicators of stream permanence to aid in jurisdictional determinations for headwater streams. We evaluated salamanders as permanence indicators because they are often abundant in fishless headwaters. Salamander and habitat data were collected in spring and summer 2003 from 59 sites located longitudinally along 17 forested streams in KY, IN, and OH. Larval Eurycea bislineata/cirrigera dominated all forests, and their abundances were highly correlated with drainage areas and channel dimensions. Appalachian streams were more diverse and had intermittent sites with more Desmognathus and Gyrinophilus spp. Of 22 sites where larvae were collected in spring, 9 sites subsequently dried in summer, suggesting salamanders either emigrated or died. We therefore only used taxa with multi-year larval stages as indicators of perennial water. Salamander larvae >1 yr old were collected from each locality in drainage areas <0.17 km2. However, these older larvae were often found in isolated pools that serve as refugia during dry periods. Findings suggest salamanders with multi-year larval periods can indicate perennial waters and that their use is more effective in Appalachia where abundance and diversity are high. Although this work was reviewed by EPA and approved for publication, it may not necessarily reflect official Agency policy.
NB22B-05 11:30h
Aquatic Insect Emergence in Post-Harvest Flooded Agricultural Fields in the Southern San Joaquin Valley, California
California's Southern San Joaquin Valley is one of the most important waterbird areas in North America, but has suffered a disproportionate loss of wetlands when compared to other California regions. This project analyzes the habitat value of post-harvest flooded cropland by measuring the emergence of aquatic insects across multiple crop types. Aquatic insect emergence was sampled from post-harvest flooded fields of four crop types (alfalfa, corn, tomato, wheat), August-October, 2003-2004. Emergence was measured using traps deployed with a stratified random distribution to sample between and within field variation. Emergence rate and emergent biomass was significantly higher in flooded tomato fields. Results from corn fields indicate that flooding depth was correlated (r=0.095) with both diel temperature fluctuation and emergence rate. Chironomus dilutus larvae were grown in environmental chambers, under two thermal treatments with the same mean but different amplitudes (high: 15°-32°C, low: 20°-26°C) to investigate thermal fluctuation effects on survival and biomass. Larval survival (4x) and biomass (2x) were significantly greater in the low versus high temperature fluctuation treatment. This research has the potential to affect agricultural management throughout the 12,600 km2 region, increase aquatic insect production and aid in the recovery of declining bird populations.
NB22B-06 11:45h
Effects and Non-effects of Stream Drying on Stonefly(Plecoptera) Assemblages in two Ouachita Mountains,AR, Catchments
Streams integrate landscape change. To establish baseline conditions and predictive relationships in two experimental catchments, we collected adult stoneflies at 38 sites for a year. We used a stratified random sampling design and regular collections of adults, which are identifiable to species level, to ensure thorough coverage. We collected 43 species (1-27 per site). We characterized sites by two descriptors: stream size as drainage AREA, and DRY, a time-weighted average of absence of surface water in measured sections. Sites ranged from continuous surface flow to partial or total drying for months. Species composition (NMS ordination) was influenced strongly by DRY. Richness of species and genera were well described (R2>85%) by multiple regressions on AREA and DRY. However, species richness was related strongly to AREA (P<0.001) but independent of DRY (P>0.45). Generic richness, in contrast, was related significantly(P<0.001)to both descriptors but the negative effect of DRY was stronger. Seasonal drying is common in the Ouachita region and part of the fauna is resistant to drying. Our results have implications for diversity-stress relationships and taxonomic resolution in community ecology and monitoring.