Hypolimnetic phosphorus and nitrogen dynamics in a small, eutrophic lake with a seasonally anoxic hypolimnion

Abstract

In situ estimates of sediment nutrient flux are necessary to understand seasonal variations in internal loading in lakes. We investigated the sources and sinks of nutrients in the hypolimnion of a small (0.33 km 2 ), relatively shallow (18 m max. depth), eutrophic lake (Lake Okaro, New Zealand) in order to determine changes in sediment nutrient fluxes resulting from a whole lake sediment capping trial using a modified zeolite phosphorus inactivation agent (Z2G1). Sediment nutrient fluxes in the hypolimnion were estimated as the residual term in a nutrient budget model that accounted for mineralisation of organic nutrients, nutrient uptake by phytoplankton and mixing, nitrification, adsorption/desorption and diffusion of dissolved nutrients at the thermocline. Of the total hypolimnetic phosphate and ammonium fluxes during one period of seasonal stratification (2007-08), up to 60 and 50%, respectively, were derived from the bottom sediments, 18 and 24% were due to mineralisation of organic species, 36 and 28% were due to phytoplankton uptake and 9 and 6% were from diffusion across the thermocline. Adsorption/ desorption of phosphate to suspended solids and nitrification were of minor (\8%) importance to the total fluxes. Any reduction in sediment nutrient release by Z2G1 was small compared with both the total sediment nutrient flux and the sum of other hypolimnetic fluxes. Uneven sediment coverage of Z2G1 may have been responsible for the limited effect of the sediment capping layer formed by Z2G1.

A Review of the Effect of Trace Metals on Freshwater Cyanobacterial Growth and Toxin Production

“…Sediments act as both a source and a sink for nutrients including trace metals in aquatic ecosystems and play a significant role in determining nutrient availability [36,49]. Thermal stratification of the water column often causes hypoxia below the thermocline, stimulating the release of nutrients such as phosphorus, nitrogen and iron from anoxic sediments [49,50,51]. Thermally stratified conditions also favour the proliferation of cyanobacteria whose buoyancy regulation may allow vertical migration to access nutrients at the sediment/water interface [22,36,52,53].…”

“…Thermally stratified conditions also favour the proliferation of cyanobacteria whose buoyancy regulation may allow vertical migration to access nutrients at the sediment/water interface [22,36,52,53]. Additionally, when the waterbody undergoes a mixing event, the nutrient rich hypolimnial water is transported to the surface via upwelling, thereby increasing nutrient availability to cyanobacteria [50]. For example, a cyanobacterial bloom in the Fitzroy impoundment near Rockhampton, Australia, was at least partially attributed to upwelling of nutrient-rich, anoxic, hypolimnetic waters into the surface layer.…”

Restraint of enzymolysis and photolysis of organic phosphorus and pyrophosphate using synthetic zeolite with humic acid and lanthanum

“…Not only can OP and PP be hydrolyzed into PO 4 3− by various phosphatases [15], but they can also be degraded by %OH in natural water under sunlight [16]. The progress in reducing PO 4 3− loads is invalid, however, because the sustained degradation of internal OP and/or PP continues to perform a key function in maintaining eutrophic status [2,17,18]. The comprehensive identification and control of potentially sedimentary bioavailable P (besides PO 4 3−…”

Storm-triggered, increased supply of sediment-derived phosphorus to the epilimnion in a small freshwater lake

“…Phosphorus is released from iron-rich sediments as a result of changes in oxygen conditions at the sedimentwater interface (Nürnberg 1984, Jeppesen et al 2005, Kagalou et al 2008, Nürnberg 2009, Özkundakci et al 2011, Loh et al 2013, Penning et al 2013. In lakes that stratify for prolonged periods during summer under generally stable meteorological conditions, sediment-derived P may be effectively trapped in the hypolimnion and thus have little or no impact on the epilimnion (Nürnberg 2009).…”