Charles L. Dow

Uptake of nutrients and organic C in streams in New York City drinking-water-supply watersheds

Abstract Uptake of nutrients and organic C was measured once annually between 2000 and 2002 in each of 10 streams within the water-supply source areas for New York City. Nutrients (PO43– and NH4+) and organic C (glucose and arabinose) were injected into the streams for 1 to 2 h, and uptake lengths were estimated from the longitudinal declines in downstream concentration relative to that of a conservative tracer. Uptake lengths increased with stream size and were converted to uptake velocities, Vf, to remove scaling effects. Vf s of PO43– and NH4+ varied inversely with the ambient concentration of total dissolved P (TDP) and total dissolved N (TDN), respectively, and were described by a model based on Michaelis–Menten kinetics. However, Vf s of glucose and arabinose were unrelated to the concentrations of any solute. Vf s of PO43–, NH4+, arabinose, and (with less certainty) glucose varied positively with measures of ecosystem metabolism (24-h community respiration and gross primary productivity). Uptake flux (U) of NH4+ also varied positively with ecosystem metabolism, but Us of PO43–, glucose, and arabinose did not. The Vf s of PO43– and NH4+ were positively related to invertebrate species richness and % forest cover, and negatively related to molecular tracer concentrations (polyaromatic hydrocarbons and fecal steroids [PO43–-Vf], fragrance materials [NH4+-Vf]) and population density. Spiraling, as a measure of ecosystem function, was sensitive to human impacts, most clearly through responses to nutrient loadings, but very probably through responses to other impacts as well.

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.

Organic matter transport in New York City drinking-water-supply watersheds

Abstract Organic matter (OM) in streams that provide drinking water is a potential energy source for bacterial regrowth in distribution systems and a precursor for disinfection byproducts. Baseflow concentrations of OM were measured over a 3-y period in 60 streams divided evenly between water-supply regions east and west of the Hudson River (EOH or WOH) in New York State. A baseline of OM concentrations in the 2 regions was generated, and land use/cover variables were related to those baseline concentrations. Dissolved organic C (DOC), biodegradable DOC (BDOC), and particulate OM (POM) reflected regional differences in land use and point-source discharges. Three-year mean concentrations for these variables and for total organic C (TOC) were significantly lower in the WOH than in the EOH by factors of 1.5 to 2.3. Size fractionation of POM showed similarities between regions with >70% of particles in the 0.5- to 10-μm size class. DOC made up most of the TOC in both regions, and DOC:POC ratios ranged from 1.7 to 54.4. Stepwise multiple linear regressions revealed that agriculture and forest land uses explained most of the variation in OM concentrations in the WOH, whereas wetlands and point-source discharges, primarily associated with wastewater treatment plants, explained most of the variation in OM concentrations in the EOH. Despite the potential problems from OM for drinking water quality, OM is a natural and important component of stream ecosystems, so its total elimination from watersheds is neither advisable nor possible. Our data from watersheds in the WOH region with high percentages (>97%) of forested land use and from small to mid-sized watersheds in the EOH with no point-source discharges provide lower limits for OM concentrations and targets for best management practices.

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.

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.

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.

Primary productivity in receiving reservoirs: links to influent streams

Abstract Primary productivity and chlorophyll a concentrations were measured in 8 reservoirs in New York City drinking-water-supply watersheds. The light-and-dark bottle O2-change procedure was used to measure gross primary productivity (GPP) once each summer from 2000 to 2002. GPP normalized for photosynthetically active radiation (PAR) in the Neversink and Schoharie averaged only 0.025 and 0.035 g O2/mol quanta, respectively. Values for New Croton and Cannonsville averaged 0.118 and 0.125 g O2/mol quanta, respectively. Values in the other reservoirs (west basin Ashokan, Pepacton, Rondout, and Kensico) were intermediate. Chlorophyll a concentrations in reservoir photic zones ranged from mean values of <10 to 100 mg/m2, with highest values in New Croton and Cannonsville and lowest concentrations in Neversink, Pepacton, and Schoharie. Cannonsville was eutrophic, and New Croton was at the mesotrophic–eutrophic boundary. Neversink, Schoharie, and Pepacton were at the oligotrophic–mesotrophic boundary, and the remaining reservoirs (Kensico, Rondout, and west basin Ashokan) were mesotrophic. Reservoir conditions were related to watershed-scale land use. Gradients within reservoirs in chlorophyll a, depth of photic zone, and primary productivity indicated an influence of the major tributary on reservoir conditions in several of the reservoirs.

Enhanced source-water monitoring for New York City: summary and perspective

Abstract Distributing 4.5 billion liters of clean fresh water every day to >9 million New York City (NYC) and suburban residents and countless other users is an enormous task that is made even more difficult by the aspiration to supply that water without filtration. To accomplish that task with a sense of confidence requires adequate data to: 1) gauge the quality of water in the source streams, 2) measure changes in that quality over time, and 3) assess the factors that might contribute to future degradation. The primary goal of the Stroud Water Research Centers large-scale enhanced water-quality monitoring project (the Project) described in the papers in this special series was to create a baseline of water quality and ecosystem health for the streams and reservoirs that provide drinking water to NYC and to relate current conditions to land use/cover. The results show that streams and rivers located west of Hudson River (WOH) deliver good to very good water to most of the receiving reservoirs. The project confirmed the eutrophic condition of the WOH Cannonsville reservoir and further linked that condition to nutrient inputs from the West Branch Delaware River. The project also confirmed that many streams located east of Hudson River (EOH) had fair to poor water quality and that streams in the Croton and Kensico watersheds were biologically and functionally degraded. Streams in some parts of the WOH region appear to be on a trajectory toward conditions already present in streams in the EOH region. Anthropogenic changes in land use from forested to agricultural in the WOH region have affected water chemistry, macroinvertebrate community structure, and stream function, although the impact is less than that caused by changes in land use from forested to urban in the EOH region. Understanding the processes of change in both regions should improve conservation, restoration, and best management practices by revealing the causes of problems, the extent and nature of those problems, and the type of landuse conditions that lead to water-quality degradation. The addition of novel parameters such as nutrient spiraling and whole-stream metabolism to traditional biomonitoring tools has established a new bridge between basic and applied research at the ecosystem level.