INVESTIGATION OF STRATIFICATION AND BOTTOM WATER HYPOXIA IN AN ESTUARINE SYSTEM

FUNDAMENTAL RESEARCH GRANT SCHEME (FRGS)

PROJECT LEADER: DR. NOOR BAHARIM HASHIM

PROJECT MEMBERS: ASSOC. PROF. DR. RAZALI ISMAIL, MAZNAH ISMAIL, AND ANIE RAFLIKHA ABD MALEK

KEYWORDS: DO depletion, stratification, hypoxia, estuary

INTRODUCTION

The severity of dissolved oxygen (DO) depletion in the bottom waters of estuaries appears to range widely depending on a combination of factors, including morphology, vertical density stratification, and perhaps nutrient and organic matter inputs. Persistent bottom-water hypoxia (DO less than 3.0mg/l) is common in stratified estuaries that have deep channels. Examples include Chesapeake Bay (Kuo et al, 1991), Puget Sound System (Christensen and Packard, 1976), and Langat River Estuary (Hashim et al.,2004). Coastal ocean areas such as the Atlantic inner continental shelf south of Long Island, New York (Falkowski et al.,1980) and northern Gulf of Mexico (Boesch 1983) also have experienced severe hypoxia. In shallow estuaries, wind mixing tends to decrease water column stratification more frequently, so that bottom water hypoxia is generally of short duration and limited in spatial extent. In Mobile Bay, USA, for example, periods of stratification and mixing occur as frequently as daily (Schroeder et al. 1990). Given the stratification is a key factor in the establishment of hypoxia, there is an obvious need for better description and quantification of the roles of freshwater discharge, lunar tides, and winds as physical energy inputs influencing vertical mixing. But, so far, only a few such studies have been conducted in Malaysia and other countries. Hypoxia has been observed frequently in the Skuadai River Estuary (Hashim et al, 2004), Langat River Estuary (Hashim et al, 2004) and parts of the Johor River Estuary (Hitech Master Corporation, 2003). Aquatic organisms are stressed by oxygen deficiency; the risk of damage to aquatic populations increases as concentration of DO deviate from saturation values. It has been reported that in Pulai River Estuary, aquaculture industries has been affected by the quality of estuarine waters. Most fish kills in the estuary in recent years have been attributed to hypoxia in the bottom waters. Hence, there is a need to examine the roles of freshwater discharge, tides, and winds influencing vertical mixing and causing stratification – destratification and hypoxia in an estuary.


OBJECTIVES

1) To determine the severity of dissolved oxygen depletion in the surface and bottom waters of an estuarine system.
2) To examine the relationships among bottom water oxygen, vertical stratification and the factors responsible for stratification-destratification in an estuarine system.


METHODOLOGY



EXPECTED RESULTS

It is expected that significant relationships exist among the variables. It is expected to benefit governmental agencies, such as Fisheries Department and Department of Environment on how stratification-destratification can affect the water quality parameters in the estuary. The relationships among the variables help determine the causes of water quality problems, fish kills, loss of seagrass beds, and reduction of aquatic lives population. The collected data and the relationships among the variables will give useful information on future development of hydrodynamic and water quality models for the estuary.

The finding will provide potentially important implications for management of the living resources of the estuary. For example, the oxygen patterns may explain why oyster, fish larvae or clams propagation historically is much better in one area than the other tidal rivers.The analysis in the study can reveal that hypoxia and stratification are caused by a combination of physical and biogeochemical processes. The results may demonstrate the changes that occur in the salinity structures as a result of freshwater inflow events, with the possible implications for the biota. The determination of phytoplankton standing stock and primary production is important which supports several economically valuable fisheries. The collected data and the finding of this study will help the long term goals of the study to develop quantitative understanding of the estuaries’s circulation and marine ecosystem, and of the sensitivity of the physical and biological system to natural and human perturbations; and to develop models of the estuaries that can aid agencies with responsibilities for environmental management in making informed decisions and serve as marine science education tools.