Abstract
Periphyton associated with plant surfaces and sediment may influence nutrient concentrations in the surface water of wetlands as periphyton biomass may change in the course of the year resulting in nutrient uptake from orrelease to the water. Between April 1996 and February 1998, the seasonal variation of periphyton biomass and nutrient content in a Dutch wetland system used for polishing effluent from a sewage treatment plant (STP) was studied. Periphyton samples were collected from emergent macrophytes stands, submerged macrophytes stands and comparable situations without vascular macrophytes. These stands were within ditches with hydraulic retention times of 0.8 or 9.3 days, which corresponded with nutrient mass input rates of approximately 1500 g N m-2 yr-1 and 350 g P m-2 yr-1, and 120 g N m-2 yr-1 and 30 g P m-2 yr-1, respectively. Light availability in the water column was an important factor regulating periphyton biomass. After a period with high periphyton living biomass, and nitrogen and phosphorus content during winter and spring, a strong light attenuation by emergent macrophytes or submerged and floating macrophytes coincided with a decrease in periphyton during the growing season. After senescence and cutting of the emergent macrophytes in autumn, light availability and periphyton biomass increased again in winter. In stands without vascular macrophytes, periphyton biomass was highest in summer. The chlorophyll-a content of periphyton associated with sediment (142-2006 mg/m2 substratum area) was always considerably higher than that of periphyton on plant shoots in the same stands, which was probably related to higher nutrient availability, less exposure to current and/or longer survival of the algae in the sediment. Year-to-year differences occurred in periphyton biomass on shoots of Phragmites australis and Typha latifolia. Maximum chlorophyll-a content of periphyton observed during this study was, however, higher on Phragmites shoots (327 mg/m2) than on Typha shoots (93.0 mg/m2). Periphyton N and P contents on Phragmites shoots were higher in a ditch with a hydraulic retention time of 0.8 days than in a ditch with a hydraulic retention time of 9.3 days. This was the result of higher uptake of nutrients by periphyton at the higher nutrient mass input rate of the ditch with a short retention time. In contrast, living algal biomass and nutrient content of periphyton on Typha shoots were higher at the longer hydraulic retention time, which was related to the lower current velocity (mean current velocity in front ditch sections 0.40 and 0.03 cm/s at a hydraulic retention time of 0.8 and 9.3 days, respectively) preventing the attached algae from being washed away from the shoots of Typha latifolia. Periphyton biomass associated with the sediment also seemed to be negatively affected by a shorter hydraulic retention time. Changes in periphyton nutrient content between sampling dates had only a small impact on nutrient dynamics of the through-flowing water in Phrgmites and Typha stands at the shorter hydraulic retention time, for which the ditches were designed. The changes in nutrient content of periphyton associated with the plant shoots and the sediment were smaller than 1 and 5 % of the STP effluent nutrient mass input rate of these stands, respectively. These values were approximately five times higher at the longer hydraulic retention time.
| Original language | English |
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| Pages (from-to) | 361-392 |
| Number of pages | 32 |
| Journal | Archiv fuer Hydrobiologie Supplement Monographic Studies |
| Volume | 139 |
| Issue number | 3 |
| Publication status | Published - 2003 |