Spatial and temporal trends in summertime climate and water qualityindicators in the coastal embayments of Buzzards Bay, Massachusetts

[摘要] Degradation of coastal ecosystems by eutrophication is largely defined bynitrogen loading from land via surface water and groundwater flows. However,indicators of water quality are highly variable due to a myriad of otherdrivers, including temperature and precipitation. To evaluate these drivers,we examined spatial and temporal trends in a 22-year record of summer waterquality data from 122 stations in 17 embayments within Buzzards Bay, MA(USA), collected through a citizen science monitoring program managed byBuzzards Bay Coalition. To identify spatial patterns across Buzzards Bay'sembayments, we used a principle component and factor analysis and found thatrotated factor loadings indicated little correlation between inorganicnutrients and organic matter or chlorophyll a (Chl a) concentration. Factorscores showed that embayment geomorphology in addition to nutrient loadingwas a strong driver of water quality, where embayments with surface waterinputs showed larger biological impacts than embayments dominated bygroundwater influx. A linear regression analysis of annual summertime waterquality indicators over time revealed that from 1992 to 2013, mostembayments (15 of 17) exhibited an increase in temperature (mean rate of0.082 ± 0.025 (SD) °C yr⁻¹) and Chl a (mean rate of0.0171 ± 0.0088 log10 (Chl a; mg m⁻³) yr⁻¹, equivalentto a 4.0 % increase per year). However, only seven embayments exhibited anincrease in total nitrogen (TN) concentration (mean rate 0.32 ± 0.47(SD) µM yr−1). Average summertime log₁₀(TN) andlog₁₀(Chl a) were correlated with an indication that the yield of Chl a per unit total nitrogen increased with time suggesting the estuarine response toTN may have changed because of other stressors such as warming, alteredprecipitation patterns, or changing light levels. These findings affirm thatnitrogen loading and physical aspects of embayments are essential inexplaining the observed ecosystem response. However, climate-related stressorsmay also need to be considered by managers because increased temperature andprecipitation may worsen water quality and partially offset benefitsachieved by reducing nitrogen loading.

[学科分类] 地球化学与岩石