Internal Phosphorus Loading in Shallow Lakes: Importance and Control

Sedimentary phosphorus in a cascade of five reservoirs (Lozoya River, Central Spain)

“…The amount of dissolved phosphate released into the water depends on many factors, including interactions with calcium (Ca), organic matter, iron, and humic materials, which play a significant role depending on the catchment geology and trophic status (Andersen andJensen 1992, Gatcher andMeyer 1993;Nurnberg 1998;Wang et al 2004). Further, resuspension of particles determine the increased amount of phosphorus released to the water in dissolved and particulate forms (Shantz et al 2004;Welch and Cooke 2005). The release of phosphorus from sediments (i.e., internal loading) may further facilitate cyanobacterial blooms, as reported in several water bodies (Hyenstrand et al 1998;Johnston and Jacoby 2003;Wang et al 2005).…”

Hydrology and water quality of Shell Lake, Washburn County, Wisconsin, with special emphasis on the effects of diversion and changes in water level on the water quality of a shallow terminal lake

“…The impact of internal phosphorus loading in delaying the response in a lake's productivity to decreases in external nutrient loading has been documented in several lakes (Larsen and Mercier 1976;others, 1979 andRobertson and Rose, 2008). This conclusion also is in agreement with the belief that once a polymictic lake becomes eutrophic, it is difficult to alter its trophic state because the high internal phosphorus loading usually does not quickly respond to reductions in external phosphorus loading (Newton and Jarrell, 1999;Nurnberg, 1998;Welch and Cooke, 1995). However, if the reduction in the external load to Shell Lake were to persist for a long period of time, the internal phosphorus release rate should gradually decrease and come to equilibrium with the new external loading.…”

“…Typically, in deeper, dimictic lakes, phosphorus released from the deep sediments is retained in the hypolimnion of the lake and is released to the shallower epilimnion primarily at fall turnover. Therefore, phosphorus concentrations near the surface (termed "near-surface concentrations") in dimictic lakes usually remain stable or decrease as summer progresses (Welch and Cooke, 1995). In polymictic lakes, however, phosphorus that is released from the sediments is frequently delivered to the surface of the lake throughout summer.…”

“…In polymictic lakes, however, phosphorus that is released from the sediments is frequently delivered to the surface of the lake throughout summer. The frequent mixing results in near-surface concentrations of phosphorus increasing throughout summer and the lake being more productive in late summer than earlier in the year (Welch and Cooke, 1995). Several factors affect the rate at which phosphorus is released from the bottom sediments.…”

“…Once phosphorus concentrations in the bottom sediments of polymictic lakes become elevated, a condition that tends to increase internal loading, the lakes usually do not respond quickly to decreases in external phosphorus inputs (Welch and Cooke, 1995;Nurnberg, 1998;Newton and Jarrell, 1999).…”