Ecology of Estuaries

Anthropogenic Effects

Michael J. Kennish

• Publisher: CRC Press
• Year: 2019
• ISBN:
  9781000722635
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Marine Biology
• Index: Biological Sciences

Ecology of Estuaries represents the most definitive and comprehensive source of reference information available on the human impact on estuarine ecosystems. The volume discusses both acute and insidious pollution problems plaguing these coastal ecotones. It also provides a detailed examination of the deleterious and pervasive effects of human activities on biotic communities and sensitive habitat areas in estuaries. Specific areas covered include organic loading, oil pollution, polynuclear aromatic hydrocarbons, chlorinated hydrocarbons, heavy metals, dredging and dredged-spoil disposal, radionuclides, as well as other contaminants and processes. The diverse components of these anthropogenic influences are assembled in an organized framework and presented in a clear and concise style that facilitates their understanding.

1 Organic Loading

Introduction

The significance of nutrient and carbon inputs (i.e., organic loading) to estuarine and marine ecosystems has been the subject of detailed investigations for decades.^1,2,3,4,5 While eutrophication resulting from continued enrichment of organic and inorganic nutrients has unequivocally compromised the water quality of many hectares of estuaries worldwide, the total impact attributable solely to sewage wastes is difficult to determine because other contaminants usually accompany high organic loads and may obfuscate their effects.⁶ Moreover, the complexity of circulation in estuaries and nearshore oceanic regions has far-reaching implications for the dilution, transport, and distribution of pollutants.^7,8 The concentration, chemical form, and availability of contaminants are dependent on the biological, chemical, and physical processes occurring in the environment and are, consequently, estuary specific.⁹ The assimilative capacity of a particular system for nutrient enrichment remains finite, and although small additions of nitrogen and phosphorus compounds commonly enhance its productivity, excessive amounts can alter the species composition, diversity, and dynamics of the biotic communities.

Eutrophication Problems

Sewage

Methods of Disposal

Sewage wastes and associated nutrients enter estuaries via three principal pathways: (1) piped outfalls, (2) riverborne discharges, and (3) sewage-sludge dumping.¹⁰ Santa Monica Bay, California (U.S.) receives treated wastewater from a major sewage treatment plant, Hyperion, by means of a submarine outfall system. Approximately 1.6 × 10⁶ m³/d of mixed primary-secondary effluent diffuses into the bay.¹¹ Over the past 40 years, the length of the discharge pipes has increased from 1.6 km offshore with the outfall at 13.7 m depth to 8 km offshore and 70 m depth for effluent and 11 km offshore and about 100 m depth for the processed solids. The monitoring of total coliform bacteria in the vicinity of the outfalls has revealed high water quality despite increased flows and waste loads in recent years.

In spite of the lower initial sewage concentrations derived from riverborne inputs than from direct pipeline discharges, increased nutrient levels and dissolved and particulate organic constituents in riverine flows ascribable to sewage enrichment can greatly influence water quality conditions in estuaries and nearshore oceanic areas, especially in proximity to large metropolitan centers. Another important difference between indirect riverborne inputs and direct pipeline discharges regards the state of the nitrogen, phosphorus, and other nutrient elements in the sewage effluent. In riverine systems, the nitrogen from sewage may be as plant bio-mass or as nutrients released by microbial decomposition of organic products. Because autotrophs assimilate some of these nutrients while being transported downstream, only a fraction of the nutrients may ultimately enter estuaries and coastal waters by this pathway. In pipeline discharges, however, the nitrogen primarily occurs in combined, unoxidized, and partially oxidized forms.¹⁰

Two examples of riverborne inputs include the River Mersey, which flows into Liverpool Bay (England), and the Raritan River, New Jersey, which empties into Raritan Bay (U.S.). The discharges of the River Mersey contain a combination of domestic sewage, industrial wastes, and agricultural runoff. The Raritan River likewise carries a wide range of contaminants from untreated and treated domestic sewage to discharges from various upriver agricultural, industrial, and manufacturing sites.¹² The Hudson-Raritan estuary complex represents a large source of nitrogen, phosphorus, and carbon for the coastal waters of the New York Bight. Only a small amount of nitrogen entering this estuary (approximately 10%) fuels primary production within the system;^13,14,15,16 most of the nitrogen flushes into surface waters of the New York Bight apex.¹⁷ Up to 80% of the available nitrogen in the apex is used by phyto-plankton within 20 km of the mouth of the Hudson-Raritan estuary.^9,18 Sewage and industrial effluents released from the Hudson and Raritan Rivers possibly contribute to episodic blooms (i.e., 100,000 cells per milliliter) of “red tide” flagellates in the apex, and in mid-summer, periods of dissolved oxygen depression and nearly anaerobic water occasionally develop in the lower estuary and apex by the decomposition of organic matter following this excess plant growth. Anoxia in the benthos of the apex may arise from seasonal and annual variations in productivity and stratification of the water column.¹⁷

Sewage sludge dumping directly affects the seabed and the benthic community. Additionally, water quality over sewage sludge dumping grounds is generally enriched in nitrogen and phosphorus which can lead to eutrophic conditions. Topping¹⁰ alluded to four well-documented sewage sludge dumping grounds, the outer Thames, New York Bight, Liverpool Bay, and Garroch Head (near Glasgow). The impact of sludge-derived nutrients on the water quality at each locale has been coupled to turbulence and water exchange. According to Topping (p. 325),¹⁰

“…In the Outer Thames, nutrients are rapidly dispersed into water that is already substantially enriched and a very large area of enhancement results masking any local effects. In New York Bight, there is better dispersal into clean renewing water and, therefore, much less nutrient build-up, but the pattern of various highly polluted inputs creates highly variable water quality situations which, however, seldom achieve major plankton anomalies because of the rapidity of water renewal. In Liverpool Bay, dispersal is only moderate and highly variable but somewhat more persistent water quality anomalies are common. Since these are associated with some toxic or unfavorable conditions, phytoplankton development is poor and favors the growth of Phaeocystis, improving towards modest diatom growth when more offshore water types are present. At Garroch Head, dispersal is poor but the water is deep and the build up of nutrients in the water column is, therefore, much less. The low level of near-bottom turbulence retains much of the nutrients in the sludge to leak away slowly. Moderately enhanced phytoplankton and rich Zooplankton result.”

Sewage Sludge Composition

In the past, sewage was commonly discharged to estuarine or coastal marine waters untreated either by comminution or chlorina-tion.¹⁹ Prior to being released to these habitats, the sewage may have been subjected to several processes to improve the effluent. Perkins¹⁹ and Klein²⁰ tabulate the following stages in sewage treatment:

1. Screening removes larger solids.
2. A comminutor macerates so...

Table of contents

• Cover
• Title Page
• Copyright Page
• The Author
• Dedication
• Preface
• Table of Contents
• Introduction
• 1 Organic Loading
• 2 Oil Pollution
• 3 Polynuclear Aromatic Hydrocarbons
• 4 Chlorinated Hydrocarbons
• 5 Heavy Metals
• 6 Radioactivity
• 7 Dredging and Dredged-Spoil Disposal
• 8 Effects of Electric Generating Stations
• Index