A review on nitrogen and organics removal mechanisms in subsurface flow constructed wetlands: dependency on environmental parameters, operating conditions and supporting media.

Microbial processes influencing performance of treatment wetlands: A review

Freshwater wetlands alter surface water quality in ways which benefit downstream use. This review summarizes the mechanisms of freshwater wetland interaction with sediment and nutrients that affect surface water quality. The mechanisms vary in magnitude and reversibility, and differ among wetland types. They include sedimentation, plant uptake, litter decomposition, retention in the soil, and microbial processes. Sedimentation is a relatively permanent retention mechanism whereby particulates and associated contaminants are physically deposited on the wetland soil surface. Plant uptake and litter decomposition provide short‐to long‐term retention of nutrients, depending on rates of leaching, translocation to and from storage structures, and the longevity of plant tissues. Plant litter can also provide a substrate for microbial processing of nutrients. Wetland soils sorb nutrients, and provide the environment for aerobic and anaerobic microorganisms that process nutrients. Wetland storage compartm...

Sediment and nutrient retention by freshwater wetlands: effects on surface water quality

The effects of season and hydrologic and chemical loading on nitrate retention in constructed wetlands: a comparison of low- and high-nutrient riverine systems

Riparian buffer zones (RBZ) improve water quality in different ways depending upon the pathway of delivery of water to the RBZ. Groundwater passing through the RBZ may be cleansed of nitrate and acidity due to a combination of denitrification, biostorage and changes in soil composition. Overland storm flows entering laterally from the uplands may be cleansed of suspended particulates, with adhering nutrients, inorganic toxins, and pesticides, as well as some dissolved nutrients and toxins. Sometimes these overland flows will also infiltrate within the RBZ and become a part of the groundwater, thus also obtaining the benefits associated with groundwaters in the RBZ. During stream flooding events, waters flooding out into the RBZ may also be cleansed of sediments, nutrients and toxic materials as a result of particulate trapping and the binding of materials on the leaf litter and soils within the RBZ. The RBZ is also an important source to the stream of high quality dissolved and particulate organic matter which is delivered both vertically and laterally. Forested RBZs also provide shade and evaporative cooling to streams, maintaining lower summertime temperatures critical to some biota. Factors which limit the effectiveness of the functions can be divided into internal and external. Factors external to the RBZ include watershed area and gradient, stream channel morphology, soil mineralogy and texture, bedrock type and depth, and climate. Factors internal to the RBZ include width and type of vegetation, waterlogging and organic content of soils, hydraulic conductivity, soil nutrient content and geochemistry. These water quality functions of RBZs and the factors which limit their effectiveness in various settings are reviewed from the world literature. INTRODUCTION Only a few papers which explicitly reported the results of studies of the water quality buffering effects of vegetated riparian zones were published prior to the early 1970s (Fig. 1). Although it is very difficult to draw sharp boundaries around this subject, there are now over 400 such papers and the rate of publication is about 30 to 35 papers per year. Despite this increasing rate of publication, our knowledge base concerning the water quality buffering effects of riparian zones is far from adequate. For descriptive aspects such as the removal of nitrate and particulate matter from the waters traversing the riparian zone or the release of organic matter to these waters we have considerable data but lack knowledge for how these functions change with climate or watershed management; species composition and age of the plant community; or how and when these functions will be saturated or exceeded. More fundamentally, we usually do not have an adequate understanding of the basic mechanisms involved in these processes or the controls over the rates of these processes. Lacking this understanding of mechanisms, we are in danger of being overconfident of our ability to predict system behaviour and response to major changes in inputs, invasions by exotic biota, or altered climate. With this situation in mind I will endeavour to review the world literature on riparian buffer zones, with my emphasis on streams and water quality. If we look at riparian vegetation and the soils in which they grow as a part of the landscape (Lowrance et al., 1985; Jordan et al., 1986; Correll et al., 1992), we can examine factors that control the health and functioning of these ecosystems and delimit them spatially. Some of these factors are internal or 7 Buffer Zones: Their Processes and Potential in Water Protection. Edited by N.E. Haycock, T.P. Burt, K.W.T. Goulding and G. Pinay. ISBN 0 9530051 0 0 © 1997 Quest Environmental. 2

Peter Cullen

Papers

Denitrification in a natural wetland receiving secondary treated effluent