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Hood Canal, Washington, USA, is a poorly ventilated fjord-like sub-basin of Puget Sound that commonly experiences hypoxia. This study examined the influence of watershed soils, vegetation, physical features, and population density on nitrogen (N) export to Hood Canal from 43 tributaries. We also linked our watershed study to the estuary using a salinity mass balance model that calculated the relative magnitude of N loading to Hood Canal from watershed, direct precipitation, and marine sources. The overall flow-weighted total dissolved N (TDN) and particulate N input concentrations to Hood Canal were 152 and 49 μg l, respectively. Nitrate and dissolved organic N comprised 64 and 29% of TDN, respectively. The optimal regression models for TDN concentration and areal yield included a land cover term suggesting an effect of N-fixing red alder ( Alnus rubra) and a human population density term (suggesting onsite septic system (OSS) discharges). There was pronounced seasonality in stream water TDN concentrations, particularly for catchments with a high prevalence of red alder, with the lowest concentrations occurring in the summer and the highest occurring in November-December. Due to strong seasonality in TDN concentrations and in particular stream flow, over 60% of the TDN export from this watershed occurred during the 3 month period of November-January. Entrainment of marine water into the surface layer of Hood Canal accounted for ≈98% of N loading to the euphotic zone of this estuary, and in a worst case scenario OSS N inputs contribute ≈0.5% of total N loading. Domestic wastewater discharges and red alders appear to be a very important N source for many streams, but a minor nutrient source for the estuary as a whole. [ABSTRACT FROM AUTHOR]

We collected suspended particulate matter (seston) and zooplankton samples from Lake Washington in Seattle, Washington, USA, over a 10-month period to investigate the effects of food availability on zooplankton fatty acid (FA) composition. The percentage of nutritionally critical ω3 polyunsaturated fatty acids (PUFA) in the seston varied from 8% of the FA pool in midsummer to 30% during the spring diatom bloom. Zooplankton accumulated much higher percentages ω3 PUFA than was available in the seston. In particular, cladocerans preferentially accumulated eicosapentaenoic acid (EPA, 20:5ω3), copepods accumulated docosahexaenoic acid (DHA, 22:6ω3), and both copepods and cladocerans accumulated 18 carbon chain ω3 PUFAs (C18 ω3). By comparison, the FA of zooplanktivorous juvenile sockeye salmon (Oncorhynchus nerka) were strongly dominated by EPA (12.5% ± 2.1%) and DHA (28.2% ± 8.7%). The saturated fatty acid and the arachidonic acid (ARA, 20:4ω6) composition of Diaptomus ashlandi was strongly (r2 = 0.76) and moderately (r2 0.54) correlated with the prevalence of these FAs in the seston. Furthermore, the DHA content of Diaptomus was moderately correlated with the seston's DHA content (r2 = 0.45) and very strongly correlated with seston EPA (r2 = 0.89). Since EPA was the most prevalent PUFA in the seston and DHA was the most prevalent PUFA in Diaptomus, these results suggest that Diaptomus may synthesize DHA from the EPA in their food. In general, zooplankton species in Lake Washington were strongly enriched with those FA molecules that are most physiologically important for fish nutrition (i.e., ARA, EPA, and DHA), indicating a clear mechanism by which changes in seston composition influence fisheries ecology. [ABSTRACT FROM AUTHOR]

We conducted statistical analyses of a 10-year record of stream nutrient and sediment concentrations for 17 streams in the greater Seattle region to determine the impact of urban non-point-source pollutants on stream water quality. These catchments are dominated by either urban (22-87%) or forest (6-73%) land cover, with no major nutrient point sources. Stream water phosphorus concentrations were moderately strongly (r2?=?0.58) correlated with catchment land-cover type, whereas nitrogen concentrations were weakly (r2?=?0.19) and nonsignificantly (at a<0.05) correlated with land cover. The most urban streams had, on average, 95% higher total phosphorus (TP) and 122% higher soluble reactive phosphorus (SRP) and 71% higher turbidity than the most forested streams. Nitrate (NO3), ammonium (NH4), and total suspended solids (TSS) concentrations did not vary significantly with land cover. These results suggest that urbanization markedly increased stream phosphorus concentrations and modestly increased nitrogen concentrations. However, nutrient concentrations in Seattle region urban streams are significantly less than those previously reported for agricultural area streams. [ABSTRACT FROM AUTHOR]

During a 1-year period, we sampled stream water total phosphorus (TP) concentrations daily and soluble reactive phosphorus (SRP) concentrations weekly in four Seattle area streams spanning a gradient of forested to urban-dominated land cover. The objective of this study was to develop time series models describing stream water phosphorus concentration dependence on seasonal variation in stream base flows, short-term flow fluctuations, antecedent flow conditions, and rainfall. Stream water SRP concentrations varied on average by ±18% or ±5.7 μg/L from one week to another, whereas TP varied ±48% or ±32.5 μg/L from one week to another. On average, SRP constituted about 47% of TP. Stream water SRP concentrations followed a simple sine-wave annual cycle with high concentrations during the low-flow summer period and low concentrations during the high-flow winter period in three of the four study sites. These trends are probably due to seasonal variation in the relative contributions of groundwater and subsurface flows to stream flow. In forested Issaquah Creek, SRP concentrations were relatively constant throughout the year except during the fall, when a major salmon spawning run occurred in the stream and SRP concentrations increased markedly. Stream water SRP concentrations were statistically unrelated to short-term flow fluctuations, antecedent flow conditions, or rainfall in each of the study streams. Stream water TP concentrations are highly variable and strongly influenced by short-term flow fluctuations. Each of the processes assessed had statistically significant correlations with TP concentrations, with seasonal base flow being the strongest, followed by antecedent flow conditions, short-term flow fluctuations, and rainfall. Times series models for each individual stream were able to predict ∼70% of the variability in the SRP annual cycle in three of the four streams ( r2 = 0.57–0.81), whereas individual TP models explained ∼50% of the annual cycle in all streams ( r2 = 0.39–0.59). Overall, time series models for SRP and TP dynamics explained 82% and 76% of the variability for these variables, respectively. Our results indicate that SRP, the most biologically available and therefore most important phosphorus fraction, has simpler and easier-to-predict seasonal and weekly dynamics. [ABSTRACT FROM AUTHOR]

We conducted a statistical analysis of a long-term (1964-1998) record of intra- and interannual temperature fluctuations in Lake Washington, Washington. Lake Washington has experienced a warming trend, with overall increases of 1.5 (0.045°C yr[sup-1]) and 0.9°C (0.026°C yr[sup-1]), respectively, for temperature data weighted over the surface (0-10 m) and entire lake volume. This warming trend was greatest for the period from April to September and was smallest and nonsignificant for November-February. A principal-components analysis of the long-term mean monthly temperature time series identified two independent modes of interannual variability. The first mode represented the months of the year when the lake warms and is warmest (e.g., March-October) and explained 54% of the variability in the overall time series. The second mode represented the months when the lake cools and is coldest (November-February) and explained 24% of the variability. The March-October mode was positively correlated with interannual variability in air temperatures and the Pacific Decadal Oscillation (PDO), multivariate r² = 0.65. The November-February mode was positively correlated with air temperature, PDO, relative humidity, solar radiation, and wind speed (r² = 0.83). A heat budget model indicated that long-term trends had a secondary role and interannual variability dominated, with exceptions being net long-wave atmospheric radiation and surface-emitted radiation, for which the long-term trend explained ∼25% and 53% of the total variance, respectively. An increase in incoming long-wave radiation fluxes was mainly associated with the increase in minimum daily temperatures (0.06°C yr[sup-1], r² = 0.47), especially during the March-October mode, when the linear trend accounted for 85% of the variability. [ABSTRACT FROM AUTHOR]

Features a study that tested the hypothesis that sockeye salmon in Lake Washington, Washington experience growth limitation because of content of phosphorus or specific essential fatty acids in their diet. Equations and parameter values for the bioenergetics model; Potential for food quality limitation of growth; Ratios of phosphorus to carbon for both sockeye salmon and zooplankton.

Temporal variability in lake phytoplankton is controlled largely by a complex interplay between hydrodynamic and chemical factors, and food web interactions. We explored mechanisms underlying phytoplankton interannual variability in Lake Washington (USA), using a 25-yr time series of water quality data (1975–1999). Time-series analysis and PCA were used to decompose chlorophyll data into modes of variability. We found that phytoplankton dynamics in Lake Washington were characterized by four seasonal modes, each of which was associated with different ecological processes. The first mode coincided with the period when the system was light limited (January–March) and phytoplankton patterns were driven by the amount of available solar radiation. The second mode (April–June) coincided with the peak of the spring bloom and the subsequent decline of phytoplankton biomass, and was largely controlled by total phosphorus levels and grazing pressure from cladoceran zooplankton. Evidence of co-dependence and tight relationship between phytoplankton and cladoceran dynamics were also found from July to October when a large portion of the phosphorus supply in the mixed layer was provided by zooplankton excretion. The fourth mode (November–December) was associated with the transition to thermal and chemical homogeneity and the winter phytoplankton minima (2–2.5μg/l). Finally, we examined the effects of meteorological forcing and large-scale oceanic climate fluctuations (ENSO and PDO) on phytoplankton dynamics and assessed the significance of their role on the interannual variability in the lake. [Copyright &y& Elsevier]