/pdf/treatment-wetlands-second-edition-4pf3o7i6u6.pdf

Treatment Wetlands, Second Edition

SUMMARY. 

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This review considers the internal fluxes and transformations of nitrogen and phosphorus in wetland ecosystems. Emphasis is placed on the dynamic nature of nutrient cycling and the review is slanted towards an applied perspective, namely the possible use of wetlands as sinks for unwanted nutrients.

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A number of basic concepts pertaining to wetland ecosystems are first explained. These are: successional time scales, exchange equilibria and the concepts of storage and through flow, resource consumption and supply including the ideas of new and regenerated nutrients and the nutrient spiralling concept. Much of the following review material is referenced back to these concepts.

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Descriptions of the basic pathways of nutrients through different types of wetland systems are given with the emphasis placed on the movement into and out of the major storage compartments of wetland systems.

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The problems of conversion of qualitative information (or data in concentration units) on nutrient movements and transformations, into data on mass flows are then discussed. The importance of understanding groundwater, evapotranspiration processes and the effects of floods and seasonality on mass flow calculations can be significant. Unidentified groundwater sources can dilute nutrient concentrations, and evapotranspiration can increase concentrations. The pattern of through flow can also alter nutrient levels. Increasing residence time has the effect of decreasing nutrients in the wetland outflow.

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The review then considers the effects of adding nutrients to wetlands. The concept of the loading capacity is discussed in relation to the length of time a wetland can continue to remove nutrients from through flow. Sediment accumulation and degassing are seen as the major long-term nutrient sinks. Nutrient enrichment results in biological changes to wetlands. These involve both changes in species composition and productivity. Not all are deleterious.

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The literature indicates that natural wetlands are not particularly effective as nutrient sinks when compared with conventional stripping plants but their value lies in removal of diffuse nutrient runoff at low concentrations. Dealing with this type of runoff by conventional means is not generally feasible.

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Recent studies show that artificially created wetlands can he effective systems for nutrient (particularly N) removal only if their internal removed mechanisms are understood and if these are optimized by management techniques.

Cycling and retention of nitrogen and phosphorus in wetlands: a theoretical and applied perspective

Production, Nutrient Content and Decomposition of Phragmites Communis Trin. and Typha Angustifolia L.

Emergent macrophytes take up their phosphorus exclusively from the sediment. Submerged species obtain phosphorus both from the surrounding water and from the substrate, but under normal pore and lake water phosphorus concentrations, substrate uptake dominates. Release of phosphorus from actively growing macrophytes (both submerged and emergent) is minimal and epiphytes obtain phosphorus mainly from the water. Decaying macrophytes may act as an internal phosphorus source for the lake and add considerable quantities of phosphorus to the water. A large part of the released phosphorus is often retained by the sediments. In perennial macrophytes the amount of phosphorus released from decaying shoots is dependent on the degree of phosphorus conservation within the plant. Macrophyte stands may also be a permanent phosphorus sink due to burial of plant litter. Macrophytes affect the chemical environment (oxygen, pH), which in turn has effects on the phosphorus cycling in lakes. However, the impact of aquatic macrophytes on whole-lake phosphorus cycling is largely unknown. Controlled full- scale harvesting, herbicide or herbivory experiments are almost totally lacking. Emergent macrophytes respond positively to eutrophication, but fertilization experiments have shown that nitrogen rather than phosphorus may be the key element. Submerged macrophytes are adversely affected by a large increase in the external phosphorus input to a lake. This effect may be caused by epiphyte shading, phytoplankton shading or deposition of unfavourable sediments.

Influence of aquatic macrophytes on phosphorus cycling in lakes

Selected aspects of the nitrogen nutrition of salt marsh cordgrass, Spartina alterni- flora, were investigated in Oak Island Marsh, North Carolina, USA. Nitrate was of minor importance as a nitrogen source for Spartina in this marsh as indicated by low soil interstitial water nitrate concentrations and low plant tissue nitrate concentrations and nitrate reductase activities. However, Spartina did have the capability of assimilating nitrate nitrogen when available. Interstitial water and plant tissue ammonium concentrations were 1-2 orders of magnitude > that for nitrate which strongly indicated that ammonium was the dominant inorganic nitrogen source. Leaf and root nitrogen con- stituents (total nitrogen, soluble nitrogen, ammonium, and nitrate) and nitrogen metabolism measured via glutamate dehydrogenase activity indicated that the nitrogen status of the short height form of Spartina was deficient relative to that of the tall form.

Nitrogen Metabolism in the Height Forms of Spartina Alterniflora in North Carolina

Calcium, magnesium, potassium, sodium, iron, and phosphorus concentrations were measured in rhizomes, leaves, and floral stalks of a Typha glauca community during the growth season of 1968. Leaf—length and plant—organ moisture contents were also determined and used as indicators of physiological aging. Seasonal fluctuation was found in all ions examined in the soil and plant parts analyzed. The ions studied were grouped into three categories with reference to apparent seasonal fluctuations of ionic concentrations. Concentration changes of calcium and possibly magnesium in plant tissue were inversely related to apparent changes in substrate concentration. Changes in concentration of potassium and phosphorus in floral stalks and leaves were inversely related to apparent changes in ion concentration in the rhizome, although not related to changes in the substrates. Changes in concentration of sodium and iron in all plant parts sampled were directly related, but no relationship was detected between the apparent changes in concentration in plant tissue and those in the substrates.

/pdf/seasonal-ionic-fluctuations-in-a-typha-glauca-community-lqz2f1uuht.pdf

Seasonal Ionic Fluctuations in a Typha Glauca Community

Calcium, magnesium, potassium, sodium, and phosphorus concentrations were measured in the shoots of a Phragmites communis community and its natural substrates during the growth season of 1969. Shoot length and shoot moisture were determined as indicators of physiological age. In addition, organic decay was followed by determination of the soil organic matter content and cation exchange capacity. Of the ions studied, calcium apparently increased in the shoot tissue, and magnesium, potassium, and phosphorus apparently decreased in the shoot tissue during the course of the growing season. Some speculations regarding the direction of net nutrient on flow in this community are advanced.

Tom A. O'Neill

Papers

Seasonal Ionic Fluctuations in a Typha Glauca Community

Seasonal ionic fluctuations in a Phragmites communis community

Climatic influences on active layer depth between 2000 and 2018 in the McMurdo Dry Valleys, Ross Sea Region, Antarctica