Eutrophication of Chesapeake Bay: historical trends and ecological interactions

Abstract

This review provides an integrated synthesis with timelines and evaluations of ecological responses to eutrophication in Chesapeake Bay, the largest estuary in the USA. Analyses of dated sediment cores reveal initial evidence of organic enrichment in ~200 yr old strata, while signs of increased phytoplankton and decreased water clarity first appeared ~100 yr ago. Severe, recurring deep-water hypoxia and loss of diverse submersed vascular plants were first evident in the 1950s and 1960s, respectively. The degradation of these benthic habitats has contributed to declines in benthic macroinfauna in deep mesohaline regions of the Bay and blue crabs in shallow polyhaline areas. In contrast, copepods, which are heavily consumed in pelagic food chains, are relatively unaffected by nutrient-induced changes in phytoplankton. Intense mortality associated with fisheries and disease have caused a dramatic decline in eastern oyster stocks and associated Bay water filtration, which may have exacerbated eutrophication effects on phytoplankton and water clarity. Extensive tidal marshes, which have served as effective nutrient buffers along the Bay margins, are now being lost with rising sea level. Although the Bay's overall fisheries production has probably not been affected by eutrophication, decreases in the relative contribution of demersal fish and in the efficiency with which primary production is transferred to harvest suggest fundamental shifts in trophic and habitat structures. Bay ecosystem responses to changes in nutrient loading are complicated by non-linear feedback mechanisms, including particle trapping and binding by benthic plants that increase water clarity, and by oxygen effects on benthic nutrient recycling efficiency. Observations in Bay tributaries undergoing recent reductions in nutrient input indicate relatively rapid recovery of some ecosystem functions but lags in the response of others. KEY WORDS: Eutrophication · Nutrients · Chesapeake Bay Resale or republication not permitted without written consent of the publisherChesapeake Bay is a large estuary which has undergone many changes in its ecological properties and processes in response to nutrient enrichment over the last 2 centuries. Susceptibility of the Bay to eutrophication arises in part from the long dendritic shoreline that intimately connects it to its large watershed (covering an area 15 times that of the Bay) which contains expanding human population centers and extensive agricultural activities. (Satellite image from MODIS,

Has eutrophication promoted forage fish production in the Baltic Sea?

“…Eutrophication is generally associated with negative impacts on the environment, such as toxic algal blooms, degradation of habitats, oxygen deficiency and fish kills (e.g. Kemp et al 2005;Anderson et al 2008;Díaz and Rosenberg 2008). Consequently, minimizing human-induced eutrophication is necessary in order to achieve good environmental status of marine ecosystems.…”

Modeling eutrophication and oligotrophication of shallow-water marine systems: the importance of sediments under stratified and well-mixed conditions

“…Consequently, reduction in nutrient loadings has been undertaken to reverse the trend of increasing eutrophication. However, oligotrophication did not always lead to the desired reduction in the intensity of algal blooms (Kemp et al, 2005), and the effects are not necessarily the same for different nutrients (Soetaert et al, 2006).…”

“…The anoxic waters possess unique chemical and biological characteristics, such as unusually high concentrations of dissolved inorganic nutrients and reduced substances, and the occurrence of processes is typically associated with anoxic sediments, such as denitrification (Naqvi et al, 1982), Anammox (Kuypers et al, 2005) or nitrous oxide formation (de Bie et al, 2002). The peculiar characteristics of anoxic bottom waters and the loss of metazoan benthic life (Kemp et al, 2005;Rabalais, 2005) have drastic consequences on ecosystem functioning, the oxidative status of the released nutrients, and the balance of nutrient release or retention in the sediment (Kemp et al, 1990;Childs et al, 2002).…”

Simulating Particulate Organic Advection along Bottom Slopes to Improve Simulation of Estuarine Hypoxia and Anoxia

“…Volatile, or reactive organics in the Bay are in dissolved and particulate forms and the particulate organics are also referred to as volatile solids or volatile suspended solids. We propose that volatile solids deposition to the channel bed come from other areas of the estuary, including the near-shore shallow waters, other then solely algal production and settling in the water column overlying the deep channel [2,3]. This is based on the observation that a simple mass balance of the algal production over the deep channel of the mainstem Chesapeake is insufficient for generation of the observed anoxia in the deep water.…”