Ecosystem responses to internal and watershed organic matter loading:consequences for hypoxia in the eutrophying Neuse River Estuary, North Carolina, USA

Abstract

ABSTRACT. The contrasting impacts of externally supplied (runoff) and internally generated (nutrientstimulated phytoplankton blooms) organic matter on oxygen (02) depletion were examined and evaluated in the eutrophic, salinity-stratified Neuse River Estuary, North Carolina, USA. This nitrogen (N)-limited estuary is experiencing increasing anthropogenic N loading from expanding urban, agricultural and industrial development in its watershed. Resultant algal blooms, which provided organic matter loads capable of causing extensive low O2 (hypoxic) and depleted O2 (anoxic) conditions, have induced widespread mortality of resident fin-and shellfish. Phytoplankton blooms followed periods of elevated N loading, except during extremely high runoff periods (e.g. hurricanes), when high rates of flushing and reduced water residence times did not allow sufficient time for bloom development. During these periods, hypoxia and anoxia were dominated by watershed-derived organic matter loading. Externally vs internally generated organic matter loading scenarios were examined in sequential years (1994 to 1996) to compare the differential impacts of an average discharge year ( l 0 yr mean hydrological conditions) (1994), N-stimulated summer algal blooms [1995), and a major hurricane (Fran; September 1996). The responses of primary production, hypoxia, and anoxia to these hydrologically contrasting years and resultant organic matter loadings help distinguish watershed from internal forcing of 0, dynamics and fish kills.

Past and future trends in nutrient export by 19 rivers to the coastal waters of Indonesia

“…Agricultural activities have increased N and P export from rivers to coastal waters globally (Galloway et al 2004;Seitzinger et al 2005;Diaz and Rosenberg 2008). In addition, dissolved organic carbon (DOC) and total suspended solids (TSS), including particulate nutrients, contribute to anoxia and hypoxia in coastal waters (Froelich 1988;Paerl et al 1998). In addition, environmental factors, such as changes in land use, hydrology, and climate, affect nutrient export by rivers.…”

Semi-diurnal seiching in a shallow, micro-tidal lagoonal estuary

“…Like many estuaries, the NRE has seen rapid growth along its shores and within its watershed during the past 50 years. This growth is believed to have resulted in eutrophication and long-term degradation of water quality in the NRE since nuisance algal blooms, hypoxia and fish kills have all been observed in recent years (Christian et al, 1986;Paerl et al, 1998). To help discern the role that flow has in affecting water quality variability, we have investigated the circulation characteristics in the NRE and the APES.…”

Marine ecological research in seashore and seafloor systems:accomplishments and future directions

“…Otherwise, the nature and importance of linkages among various marine and even terrestrial ecosystems are poorly known. Coastal benthiddeinersal systems are especially interesting in this regard because they are juxtaposed with the land on one side and the open sea on the other, and in both cases significant linkages between systems occur via physical (oceanic, atmospheric, riverine) and biological (mobile species) transport mechanisms (Polis et al 1997, Paerl et al 1998. New opportunities for the study of such processes are available with recent developments in isotopic analyses, remote sensing, satellite imagery, CIS technology, and instrumentation for tracking animals at sea.…”

“…An example of the potential utility of merging sclence and management IS the development of marine protected areas for the joint purpose of conserving exploited populations, assessing population-to-ecosystem-level impacts of fisheries, and determining the roles of large predatory flshes in benthiddemersal communities. While fishing is perhaps the most well known agent of anthropogenic influence on marine ecosystems, eutrophication is another process that is dramatically transforming estuari.ne and shallow coastal systems in some parts of the world (Turner & Rabalais 1994, Nixon 1995, Paerl et al 1998. Much research has been devoted to understanding the effects of nutrient loading on phytoplankton (without yet adequate understanding of the dynamics of nuisance blooms).…”

“…Much research has been devoted to understanding the effects of nutrient loading on phytoplankton (without yet adequate understanding of the dynamics of nuisance blooms). Yet the food-chain consequences of nutrient loading, and how change in productivity and composition of the microalgal assemblage alters the composi.tion, production, interactions and dynamics of consumers at higher trophic levels are unknown (Paerl et al 1998). The use of environmental management on the scales of watersheds for large-scale experiments, with resource managers working in conjuncti.on wlth marlne ecologists, holds tremendous promise for answering important questions about system dynamics and the sustainability of ecosystem services.…”