David B. Arscott

Aquatic invertebrate community structure along an intermittence gradient: Selwyn River, New Zealand

Abstract Changes in community structure and life-history traits of benthic invertebrates were examined along a longitudinal intermittence gradient in an alluvial river. The gradient was characterized with modeled and measured hydrologic, chemical, and physical environmental variables. The invertebrates were collected in the Selwyn River, southeastern New Zealand, at multiple sites in each of 4 river sections with distinct hydrological conditions (perennial-losing, ephemeral, intermittent, perennial-gaining). Values of hydrological metrics for each site were generated with an empirical model developed for the Selwyn River. The metrics included 4 that characterized intermittent flow (flow permanence, flow duration, drying frequency, distance to nearest perennial site). Most invertebrate richness and density metrics were significantly higher in the perennial-losing and perennial-gaining sections than in the ephemeral and intermittent sections. A principle components analysis (PCA) separated invertebrate samples from the 4 sections along 2 primary factors. Nine of 13 hydrological metrics, including the 4 intermittence metrics, were correlated with the PCA site scores. Linear regressions indicated that most taxon-richness metrics and some density metrics were related to flow permanence, flow duration, or both. Based on the regression analysis, we predicted that 1.9 taxa/m2 are added with each 10% increase in flow permanence, and 0.5 taxa/m2 are added with each 10-d increase in flow duration. Results from a nestedness analysis indicated that communities at ephemeral and intermittent sites were nested subsets of the communities at perennial sites, and the nesting order of sites was related to both flow permanence and flow duration. Assemblages of taxa with particular life-history traits (life span, fecundity, maximum size, and voltinism) varied linearly with flow permanence and flow duration. The variation in invertebrate communities along the Selwyn River was primarily the result of progressive removal of desiccation-sensitive taxa with increasing intermittence, not to selection for desiccation-resistant specialists. Quantitative intermittence–ecology relationships are needed to predict the consequences of future changes in flow intermittence, but such relationships are rare. The univariate relationships reported in our study contribute to a small but growing array of intermittence–ecology relationships.

Ecosystem Metabolism in Piedmont Streams: Reach Geomorphology Modulates the Influence of Riparian Vegetation

We measured the impact of riparian zone vegetation on ecosystem metabolism in paired forested and meadow reaches on 13 streams in southeastern Pennsylvania and Maryland, USA. Metabolism estimates were based on open-system measurements of dissolved oxygen changes, with reaeration determined from propane evasion. Daily gross primary productivity (GPP) in meadow and forested reaches averaged 2.85 and 0.86 g O2 m−2 d−1, respectively, at water temperatures of 12°C or greater when the forest canopy was developed and 1.74 and 1.09 g O2 m−2 d−1, respectively, at temperatures below 12°C when the canopy was bare. Community respiration (CR24) also was greater in meadow reaches than in forested reaches, averaging 5.58 and 3.57 g O2 m−2 d−1, respectively, in the warm season and 4.87 and 2.88 g O2 m−2 d−1, respectively, during the cold season. Thus, both meadow and forested reaches were heterotrophic. Forested reaches were always wider and nearly always shallower than companion meadow reaches. When ecosystem function was assessed per unit of stream length, the difference in average GPP between meadow and forested reaches was reduced from three-fold to 1.9-fold in the warm season, and mean GPP was greater in the forested reaches during the cold season. Mean CR24 per meter stream length was greater in forested reaches during both seasons. Even though riparian shading reduced primary productivity per unit area of streambed, the greater stream width of the forested reaches counteracted that reduction in part. Thus, when rates of ecosystem function were expressed per length of stream, differences between reaches were always smaller than when expressed per area, and activity per unit stream length was sometimes greater in forested reaches than in meadow reaches.

Ecosystem metabolism in streams of the Catskill Mountains (Delaware and Hudson River watersheds) and Lower Hudson Valley

Abstract Ecosystem metabolism was measured in 10 streams flowing into New York City drinking-water-supply reservoirs. Six of the streams were located west of Hudson River (WOH) in the Catskill Mountains and 4 were in the Croton River watershed east of Hudson River (EOH). Measurements were made for 3-d periods between June and November in each of 3 y using an open-system O2 technique with reaeration determined from propane evasion. Chlorophyll a concentrations, algal cover types, and nutrient uptake were measured concurrently. Gross primary productivity ranged from 2.02 to 4.32 g O2 m−2 d−1 in the WOH streams and from 0.23 to 1.13 g O2 m−2 d−1 in the EOH streams. Community respiration ranged from 3.94 to 8.30 g O2 m−2 d−1 in the WOH streams and from 1.39 to 6.12 g O2 m−2 d−1 in the EOH streams. All streams were heterotrophic. The WOH streams were larger and more open than the EOH streams. Metabolism was strongly correlated with instream environmental and water-chemistry variables and riparian shade. Land use was largely forested with some agriculture in the WOH watersheds, and it was forested or urbanized in EOH watersheds. Landuse impacts were confounded by the smaller size and denser shade along EOH streams than along WOH streams.

Macroinvertebrate distribution in relation to land use and water chemistry in New York City drinking-water-supply watersheds

Abstract Macroinvertebrate communities were examined in conjunction with landuse and water-chemistry variables at 60 sites in the NYC drinking-water-supply watersheds over a 3-y period. The watersheds are in 2 adjacent regions of New York State (east of Hudson River [EOH] and west of Hudson River [WOH]) that are geographically distinct and have unique macroinvertebrate communities. Nonforested land use at EOH sites was mostly urban (4–57%), whereas land use at sites in the rural WOH region was more agricultural (up to 26%) and forested (60–97%). Land use accounted for 47% of among-site variability in macroinvertebrate communities in the EOH region and was largely independent of geological effects. Land use accounted for 40% of among-site variability in macroinvertebrate communities in the WOH region but was correlated with underlying geology. Comparisons among 3 landuse scales emphasized the importance of watershed- and riparian-scale land use to macroinvertebrate communities in both regions. Multivariate and bivariate taxa–environment relationships in the EOH and WOH regions identified specific landuse and water-chemistry gradients and, in general, showed a continuum in conditions across the watersheds. WOH macroinvertebrate communities varied primarily with specific conductance, population density, and agricultural and urban land use, but communities were not classified as impaired along these gradients. EOH macroinvertebrate communities were associated with a wider range of watershed conditions than WOH communities. Conditions ranged from forested to urban, and distinctive communities were associated with point-source discharges, road density, and lake outlets. The severity of the impact gradient in the EOH region resulted in impaired macroinvertebrate communities with decreased total and Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxon richness and increased densities of oligochaetes and chironomids.

Role of rarity and taxonomic resolution in a regional and spatial analysis of stream macroinvertebrates

Abstract Quantitative sampling of benthic macroinvertebrate communities from 60 sites in New York Citys drinking-water-supply watersheds was undertaken in 2000, 2001, and 2002 as part of a large-scale enhanced water-quality monitoring project (the Project). Sampling yielded 543 macroinvertebrate taxonomic units, most of which (including Chironomidae) were identified to the genus/species level. Our goals were to investigate the effect of level of taxonomic resolution on statistical macroinvertebrate–environment relationships, the effect of including rare taxa on among-site similarity and macroinvertebrate–environment relationships, and the correlations between the common and rare components of the total community at each site. Mean site richness ranged from 90.8 to 101.2 taxa for sites west of Hudson River (WOH) and 62.2 to 78.5 taxa for sites east of Hudson River (EOH). Species-level identifications provided the greatest separation of sites in multivariate space, but genus- and family-level identifications discriminated between most- and least-impacted sites, particularly in the EOH region where anthropogenic impact was greatest. Of the 543 taxa, 175 (32%) were found at ≤3 sites, and nearly ½ of the taxa within a given site were occasional (found once in 3 y). Numerically rare taxa (defined as either <1% or <0.3% relative abundance within each site) accounted for 42 to 75% (WOH) and 37 to 73% (EOH) of mean site richness. Ordinations of data sets including or excluding rare taxa revealed similar impact gradients, and the % of spatial variance explained by environmental factors was similar with and without rare taxa included. Common taxa contributed noise to site-similarity patterns in the WOH region, and rare taxa provided information that was redundant with information provided by common taxa in the EOH region.

Relating major ions and nutrients to watershed conditions across a mixed-use, water-supply watershed

Abstract Stream inorganic chemistry was sampled under summer baseflow conditions from 2000 to 2002 at 60 sites as part of a large-scale, enhanced water-quality monitoring project (the Project) across New York Citys drinking-water-supply watersheds. The 60 stream sites were evenly divided between regions east and west of the Hudson River (EOH and WOH, respectively). EOH sites had generally higher ionic concentrations than WOH sites, reflecting differences in land use and geology. Within each region, variability in inorganic chemistry data between sites was far greater than annual variability within sites. Geology was an important factor controlling underlying baseflow chemistry differences within and between regions. However, after taking into account geological controls, anthropogenic land uses primarily defined ion and nutrient baseflow chemistry patterns at regional and watershed levels. In general, watershed-scale landscape attributes had either the strongest relationships with analytes or had relationships with analytes that did not differ fundamentally from relationships of riparian- or reach-scale landscape attributes. Individual analyses indicated no dominant watershed-scale landscape attribute that could be used to predict instream inorganic chemistry concentrations, and no single ion or nutrient was identified as the best indicator of a given anthropogenic land use. Our results provide a comprehensive baseline of information for future water-quality assessments in the region and will aid in examining other components of the Project.

Comparison of epilithic algal and bryophyte metabolism in an arctic tundra stream, Alaska

Phosphorus has been added to a reach of the Kuparuk River, Alaska, from late June to mid August every year since 1983. The P-fertilized reach of the river is now extensively colonized by 2 bryophytes (Schistidium agassizii and Hygrohypnum spp.), whereas only S. agassizii is common in unfertilized reaches of the river. We compared photosynthesis rates of epilithic algae, S. agassizii, and Hygrohypnum spp. under reference and P-enriched conditions to extend our long-term records of bryophyte dynamics within the fertilized reach and to describe the physiological differences between major primary producers. Rates of primary production were determined from changes in dissolved oxygen concentration during light and dark incubations of algal and bryophyte samples in closed chambers. Net primary productivity per unit total chlorophyll a (CHLt a) was greater for epilithic algae (2.0-6.0 mg O2 mg-1 CHLt a h-1) than for bryophytes (0.2-1.7 mg O2 mg-1 CHLt a h-1). However, the greater biomass of the bryophyte community in the fertilized reach yielded area-specific productivity rates for Hygrohypnum spp. that were 2 to 4 times greater than areal rates of epilithic algal productivity. Bryophytes accounted for 80% of primary production in P-fertilized reaches but only 9% in reference reaches. Thus, increased bryophyte abundance in response to P increased total net primary production from 2.3 g C/h to 6.3 g C/h. Photosynthesis-irradiance (PI) parameters obtained by fitting data to a hyperbolic tangent model differed between bryophyte species, between reference and fertilized stream reaches, and over the season. Differences in PI relationships between S. agassizii and Hygrohypnum spp. suggest that they use different life strategies (subsistence vs opportunism, respectively) to exist in the arctic environment.

Landscape template of New York City's drinking-water-supply watersheds

Abstract New York City (NYC) receives >99% of its drinking-water supply from streams, rivers, and reservoirs north and northwest of the city (east or west of Hudson River [EOH or WOH, respectively]). As part of a large-scale enhanced water-quality monitoring project (the Project) in NYCs drinking-water-supply watersheds, 60 stream and 8 reservoir sampling sites were established in the water-supply area (30 WOH and 30 EOH) and sampled from 2000 to 2002. Our study describes watershed characteristics (including climate and hydrology, land use, human population, and known point-source discharges) at each study site and provides an analysis of differences in land use quantified at 3 scales: 1) watershed, 2) riparian (30 m on each side of entire stream network upstream of a site), and 3) reach (same as riparian, but truncated 1 km upstream of the study site). Regression analysis was used to determine relationships among scales, and principal components analysis was used to describe spatial differences in watershed characteristics across the study region. EOH sites are on smaller streams than WOH sites because the WOH region is much larger than the EOH region. EOH sites had smaller mean annual area-specific discharges than WOH sites, reflecting differences in precipitation and in watershed hydrologic retention that were related to surficial geology and the presence of wetlands, lakes, and reservoirs. Population densities, point-source discharges, and flows from those discharges were higher in EOH watersheds than in WOH watersheds. Landuse values in the EOH watersheds ranged from 87% forest to 57% urban. Agricultural land use exceeded 16% in only one watershed. Landuse values in WOH watersheds indicated either largely forest (several sites near 98%) or agriculture and grassland (many near 25%, largely in pasture). Urban landuse values were never >11%. Values for most landuse categories were strongly correlated (most R2 > 0.75) between the watershed and riparian scales. In WOH watersheds, values for categories indicating human land use (e.g., agriculture, urban) were greater at the riparian than at the watershed scale, indicating that human land use was concentrated along the stream network. In EOH watersheds, values for categories indicating human land use were lower at the riparian than at the watershed scale. Values for most landuse categories were not correlated (typically R2 < 0.50 or not significant) between the reach and watershed scales, indicating that local landuse values described statistically different conditions than watershed- or riparian-scale landuse values.

Enhanced source-water monitoring for New York City: historical framework, political context, and project design

Abstract An enhanced water-quality monitoring project was established in 2000 for streams providing drinking water to New York City (NYC). The projects design considered the history of the NYC source watersheds, and some of the broader issues facing freshwater supply systems in general. NYCs relationship with its watershed has historically been acrimonious and filled with mistrust, a situation that became critical in 1989 when the US Environmental Protection Agency (EPA) issued the Surface Water Treatment Rule (SWTR), which required all unfiltered public water-supply systems either to provide filtration or to comply with a stringent set of water-quality, operational, and watershed-control standards. Plans to implement this rule caused further mistrust and lawsuits, which led in 1997 to the NYC Watershed Memorandum of Agreement (MOA), a compromise that was accepted by all the stakeholders. The MOA addressed fundamental issues about: 1) the protection, allocation, and ownership of water resources, 2) the identification and valuation of ecosystem services, 3) the compatibility of environmental protection and economic development, and 4) strategies for bringing together diverse stakeholders in the watershed. One of the provisions of the MOA was to enhance the existing city, state, and federal monitoring programs for NYCs source watersheds. The monitoring project described in this series, which is part of that enhancement, recognizes philosophically that source watersheds and their ecosystems are: 1) the ultimate source of the water, 2) the major source of anthropogenic contaminants in the water, and 3) the primary natural processors of water-borne contaminants. Protecting NYCs source-water areas requires an integrated approach that ties historical and contemporary land use into the design of a large-scale, enhanced, water-quality monitoring project (the Project). The Project set forth 4 primary objectives: 1) to create a quantitative baseline of selected physical, chemical, and biological characteristics of source-water streams and reservoirs for use in assessing future changes in the quality of NYCs drinking water and the integrity of the associated aquatic ecosystems, 2) to include in the baseline factors that are sensitive to temporal variability, are reproducible, and lend themselves to unconfounded analyses among sampling sites and times, 3) to integrate temporal and spatial change in both the level of selected contaminants and the structure and function of biological communities and ecosystems to assess whether impairment impacts the ability of the streams to provide ecosystem services related to water quality, and 4) to provide additional direction and perspective to the overall watershed management plan for the NYC source-water area. All papers in this series cover Phase I of the monitoring project, which involved physical, chemical, and biological measurements made during 2000 to 2002 at 60 stream sites distributed across a 5066-km2 study area.

Molecular tracers of soot and sewage contamination in streams supplying New York City drinking water

Abstract A molecular tracer method was used to assess the extent and sources of pollution to 60 stream sites that were distributed across the watersheds that supply drinking water to the greater New York City area. Samples were collected from each site annually from 2000 to 2002 during summer baseflow conditions. Twelve polycyclic aromatic hydrocarbons (PAH), 2 fragrance materials (FM), caffeine (CAF), and 7 fecal steroids (FS) were measured using a modification of EPA method 8270, which quantified concentrations to laboratory reporting levels ranging from 0.00009 to 0.016 μg/L or 3 to 5 orders of magnitude lower than method detection levels (MDL) given by EPA 8270. In 54 of 180 stream samples, concentrations of ≥1 PAHs exceeded suggested, nonregulatory EPA guidance values for water supplies (0.0038 μg/L for the 5 most toxic PAHs), and PAH signatures (ratios) and spatial patterns suggested that soot from local urban/suburban combustion was the primary source. CAF, FM, and FS all showed their highest concentrations at the 3 sites with large, failing sewage treatment plants, but more complex relationships to landscape variables at remaining sites suggested a variety of anthropogenic point and nonpoint sources. Concentrations of all molecular tracers measured were strongly negatively correlated with % forest cover (= all forest variables used) in the watershed.