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Spatial and temporal patterns in nutrient standing stock and mass-balance in response to load reductions in a temperate estuary.

机译：温带河口的养分减少和养分平衡的时空分布

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摘要

The addition of excess nutrients into a system , is a widespread problem in estuaries throughout much of the world. To combat this trend, many management agencies are imposing regulations limiting the amount of nutrients (nitrogen and phosphorus) which can be discharged into coastal waters through wastewater treatment and agriculture. In 2005, the Rhode Island Department of Environmental Management (RIDEM) enacted legislation mandating that wastewater treatment facilities (WWTF) discharging their effluent into Narragansett Bay and its tributaries reduce the concentration of nitrogen in their effluent. This legislation will reduce wastewater nitrogen loading to the bay by 50% by 2014 with the ultimate goal of improving water quality, reducing hypoxia, and restoring lost ecosystem services (e.g. seagrass) to the bay. Early stages of this reduction took place between 2005--2009, reducing loadings at 11 WWTF's which discharge into the bay from 16--20mg/l total nitrogen to either 8 or 5mg/l.;Response of other estuaries to similar reductions in loading has been varied and complex, with relatively few ecosystems showing straightforward linear reductions in concentration, productivity, and chlorophyll with reduced load. The overall goal of this study is to quantify the impact of these initial loading reductions on the standing stock (Chapter 1), seasonal cycling (Chapter 2), and mass-balance (Chapter 3) of nitrogen and phosphorus in Narragansett Bay.;To accomplish this goal, we first reviewed data from a five-year study of surface nutrient concentration at 13 stations throughout Narragansett Bay (Chapter 1). Because Narragansett Bay is aligned along a north-south gradient of decreasing urbanization and most sources of nutrients to the bay are located in or around the city of Providence, at the head of the estuary, we can establish down-bay relationships of nutrient constituents to see how their concentrations change spatially throughout the bay, and compare these relationships to past studies. We can also use established volume relationships to estimate the total standing stock of nutrients in the bay at any given time, and compare how this changes over the course of a year during the present survey and during past surveys. In response to a loading reduction in dissolved inorganic nitrogen of 30% and in total nitrogen of 17%, we saw measurable reductions in downbay concentrations and standing stocks approximately on par with these reductions. Phosphorus concentrations in the bay have declined dramatically (30--50%) in part due to recent loading reductions, but also in part due to management action in the 1980's and 1990's to remove phosphates from detergents and industrial surfactants. We also see changes in the way nitrate, nitrite, and ammonium are used on a downbay gradient, which we hypothesize are related to the loading reductions.;In order to fully understand the impact of load reductions on the ecosystem, we must also consider how the nutrients in the system have changed over the long-term, both in terms of annual cycling, and in terms of response to changing climate in the bay. This analysis constitutes the second chapter of the dissertation. Over the last 50--100 years, Narragansett Bay has grown measurably warmer, and weather patterns have changed, bringing increased cloud cover, more storms, and more precipitation. All of these changes impact the way nutrients enter the bay, and the way phytoplankton use the nutrients. We examined the impact of these potential changes using a long-term weekly dataset of nutrient concentrations collected by the MERL lab at the University of Rhode Island Graduate School of Oceanography since 1978. We use both conventional statistics and a state-space model formulated in the computing language R (SSPIR). Our results show virtually no long-term trend or change in timing of seasonal cycling of nutrients or chlorophyll. However, we do see changes in the seasonal patterns of concentration of both nutrients and chlorophyll at the GSO station, with measurable changes in cumulative distribution function for phosphate, silicate, ammonium, and chlorophyll. We also observe statistically significant reductions over the course of the time series for nitrate, nitrite, ammonium, and phosphate, though it is difficult to ascribe causality to these changes. Model results were largely inconclusive, but show a marginally significant intervention effect attributable to the loading reduction in the ammonium signal at the GSO dock, with no significant long-term trend observed for any analyte.;Finally, we conduct a mass-balance nutrient budget assessment for nitrogen and phosphorus in Narragansett Bay (Chapter 3). Mass-balance is a common way of tracing the sources, sinks, and reservoirs of nutrients in a system, and seeing how these components might change with time. Nutrient budgets for Narragansett Bay have been compiled approximately every decade, but recent and future loadings compel a reanalysis to determine how the system is responding to initial stage reductions. We see a reduction in WWTF loading to the bay of just over 100 million moles of nitrogen and 4 million moles of phosphorus, which constitutes about 20 and 16 percent of the net annual load of nitrogen and phosphorus from all sources. However, much of this reduction is realized in tributary rivers, and variable riverine abatement rates in those rivers mean that some of the net reduction is not felt by the bay proper. Furthermore, evidence from literature suggests that changes in bay sediment net denitrification rate may be offsetting some or all of the loading reductions.
机译：在系统中向系统中添加过多的养分是世界各地河口普遍存在的问题。为了应对这种趋势，许多管理机构都在制定法规，限制通过废水处理和农业排放到沿海水域的养分（氮和磷）的数量。 2005年，罗得岛州环境管理部（RIDEM）颁布了一项法规，要求将废水排放到纳拉甘西特湾及其支流的废水处理设施（WWTF）会降低废水中的氮浓度。这项立法将到2014年将海湾中的废水氮负荷减少50％，其最终目标是改善水质，减少缺氧并恢复海湾中失去的生态系统服务（例如海草）。这种减少的早期阶段发生在2005--2009年之间，将11个WWTF的负荷减少到海湾中的总氮从16--20mg / l降至8或5mg / l;其他河口对负荷的类似减少做出了响应种类繁多而复杂，相对较少的生态系统显示出浓度，生产力和叶绿素随负荷的降低而线性下降。这项研究的总体目标是量化这些初始负荷减少对纳拉甘塞特湾的氮和磷的现存量（第1章），季节性循环（第2章）和质量平衡（第3章）的影响。为了实现这一目标，我们首先回顾了为期5年的对纳拉甘塞特湾（Narragansett Bay）的13个站点的表面营养物浓度的研究数据（第1章）。由于Narragansett湾沿城市化程度递减的南北坡度排列，并且该湾的大部分养分来源都位于普罗维登斯市或其周围，在河口的顶部，我们可以建立养分成分与了解它们的浓度在整个海湾中如何在空间上变化，并将这些关系与以往的研究进行比较。我们还可以使用已建立的体积关系来估计任何给定时间海湾中养分的总存量，并比较当前调查和过去调查在一年中的变化情况。响应于溶解的无机氮和总氮的负荷减少了30％，我们看到可测量的下湾浓度和固定存量减少量与这些减少量相当。海湾中的磷浓度已急剧下降（30--50％），部分原因是最近的负荷减少，也部分是由于1980年代和1990年代的管理行动，目的是从洗涤剂和工业表面活性剂中去除磷酸盐。我们还看到硝酸盐，亚硝酸盐和铵盐在下湾梯度上使用的方式发生了变化，我们认为这与减载有关。为了充分了解减载对生态系统的影响，我们还必须考虑如何长期而言，无论是年度循环还是对海湾气候变化的响应，系统中的营养素都已发生长期变化。这一分析构成了论文的第二章。在过去的50--100年中，Narragansett湾已经明显变暖，天气模式发生了变化，带来了更多的云层覆盖，更多的暴风雨和更多的降水。所有这些变化都会影响养分进入海湾的方式以及浮游植物利用养分的方式。自1978年以来，我们使用罗德岛大学海洋学研究生院的MERL实验室每周收集的长期养分浓度数据集，研究了这些潜在变化的影响。我们同时使用常规统计数据和状态空间模型，计算语言R（SSPIR）。我们的结果显示，营养素或叶绿素的季节性循环几乎没有长期趋势或时间变化。但是，我们确实看到了GSO站养分和叶绿素浓度的季节性变化，磷酸盐，硅酸盐，铵和叶绿素的累积分布函数也发生了可测量的变化。我们也观察到在时间序列上硝酸盐，亚硝酸盐，铵和磷酸盐的统计显着减少，尽管很难将这些变化归因于此。模型结果在很大程度上尚无定论，但显示出归因于GSO码头铵信号负载减少的干预效果，在边际上具有显着意义，对任何分析物均未观察到明显的长期趋势。最后，我们进行了质量平衡的营养物预算评估纳拉甘西特湾的氮和磷（第3章）。质量平衡是追踪系统中养分的来源，汇和库，并查看这些成分如何随时间变化的常用方法。大约每十年都会编制纳拉甘西特湾的营养预算，但是最近和将来的负载会迫使重新分析，以确定系统如何响应初始阶段的减少。我们看到，海湾中的WWTF装载量减少了1亿摩尔以上，磷减少了400万摩尔，分别占所有来源氮和磷净年负荷的20％和16％。但是，这种减少大部分是在支流中实现的，而这些河流中可变的河流消减率意味着，海湾适当地区并未感觉到某些净减少。此外，来自文献的证据表明海湾沉积物净反硝化率的变化可能抵消了部分或全部负荷的减少。

著录项

  • 作者

    Krumholz, Jason Seth.;

  • 作者单位

    University of Rhode Island.;

  • 授予单位 University of Rhode Island.;
  • 学科 Biology Oceanography.;Environmental Sciences.
  • 学位 Ph.D.
  • 年度 2012
  • 页码 400 p.
  • 总页数 400
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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