Macrophyte-related shifts in the nitrogen and phosphorus contents of the different trophic levels in a biomanipulated shallow lake

Abstract

Lake Zwemlust, a small highly eutrophic lake, was biomanipulated without reducing the external nutrient loading, and the effects were studied for four years. In this paper we pay special attention to the shifts in relative distribution of nitrogen and phosphorus in the different trophic levels and to the changes in growth limitation of the autotrophs.Despite of the high external nutrient loads to the lake (ca 2.4 g P me2 y-' and 9.6 g N m-* y-'), the effects of biomanipulation on the lake ecosystem were pronounced. Before biomanipulation no submerged vegetation was present in the lake and P and N were stored in the phytoplankton (44% N, 47% P), fish (33% N, 9% P) and in dissolved forms (23% N, 44% P). P and N contents in sediments were not determined. In the spring and summer following the biomanipulation (1987), zooplankton grazing controlled the phytoplankton biomass and about 90 y0 of N and P were present in dissolved form in the water. From 1988 onwards submerged macrophyte stands continue to thrive, reducing the ammonium and nitrate concentrations in the water below detection levels. In July 1989 storage of N and P in the macrophytes reached 86% and SO%, respectively. Elodea nuttallii (Planchon) St.John, the dominant species in 1988 and 1989, acted as sink both for N and P during spring and early summer, withdrawing up to ca 60% of its N and P content from the sediment. At the end of the year only part of the N and P from the decayed macrophytes (ca 30 y0 of N and 60 y0 of P) was recovered in the water phase of the ecosystem (chiefly in dissolved forms). The rest remained in the sediment, although some N may have been released from the lake by denitrification.In summer 1990 only 30% of the N and P was found in the macrophytes (dominant species Ceratophyllum demersum L.), while ca 30% of N and P was again stored in phytoplankton and fish.

Existence of a macrophyte-dominated clear water state over a very wide range of nutrient concentrations in a small shallow lake

“…Elodea nuttallii (Planchon) St . John, for example, stored 86% of the available N and 80% of the available P and acted as sink both for N and P and maintained a clear water state in Lake Zwemlust (van Donk et al ., 1993) . Despite the marked reduction in total phosphorus concentrations, substantial concentrations of available soluble reactive phosphorus still remain but ammonium has declined (Carvalho et al ., 1995) and recently both ammonium and nitrate have been close to undetectable in Little Mere for much of the summer (Moss et al ., 1996) .…”

“…The macrophyte-dominated clear water state possesses a number of feedback mechanisms for stabilizing the clear water state by provision of refuges for phytoplankton grazers against fish predation (Timms & Moss, 1984), similar linkages for periphyton grazers (Leah et al ., 1978), allelopathy (Wium- Anderson, 1987), reduction of resuspension of bottom material (Bostrom et al ., 1982), and nutrient limitation of phytoplankton through nitrogen uptake by the plants or denitrification by the microorganisms associated with them (Ozimek et al ., 1990;van Donk et al ., 1993) . Macrophytes also provide spawning grounds and refuge against cannibalization for piscivorous fish like pike, which in turn decrease zooplanktivorous and benthivorous fish density (Grimm, 1989) .…”

Cyanobacterial blooms in a temperate river-floodplain ecosystem: the importance of hydrological extremes

“…In the conditions of extremely high floodings, the whole floodplain area was inundated (Fig. 1c) and the lake became the deepest part of a single large shallow water body with mass developed submerged macrophytes (Ceratophyllum demersum L., Myriophyllum spicatum L. and Potamogeton (Van Donk et al 1993;Dokulil et al 2006), producing allelopathic substances that inhibit the growth of phytoplankton (Gross et al 2007), decreasing underwater light availability (Cattaneo et al 1998), and/or creating an environment that favors small phytoplankton taxa that are easily grazed by zooplankton (Muylaert et al 2006). Altogether, our data showed that the clear water state of the investigated lake was unstable as was expected under very high nutrient loadings (Janse et al 2008).…”

Predicting the hydraulic forces on submerged macrophytes from current velocity, biomass and morphology

“…However, such clear water has not always been accompanied by spontaneous recovery of macrophyte populations. There is increasing evidence that clear and turbid water are alternative stable states at moderately high nutrient loading ) and that aquatic macrophytes can promote stability of the clear-water state by providing physical protection for grazers on the algae, by competing with the algae for nutrients and by reducing water currents and allowing suspended material to settle (Blindow et al 1993;James and Barko 1990;Moss 1990;Ozimek et al 1990; Van den Berg et al 1998;Van Donk et al 1993).…”