Phosphorus

About: Phosphorus is a research topic. Over the lifetime, 53120 publications have been published within this topic receiving 939731 citations. The topic is also known as: element 15 & P.

Does high nitrogen loading prevent clear-water conditions in shallow lakes at moderately high phosphorus concentrations?

Abstract: Summary 1. The effect of total nitrogen (TN) and phosphorus (TP) loading on trophic structure and water clarity was studied during summer in 24 field enclosures fixed in, and kept open to, the sediment in a shallow lake. The experiment involved a control treatment and five treatments to which nutrients were added: (i) high phosphorus, (ii) moderate nitrogen, (iii) high nitrogen, (iv) high phosphorus and moderate nitrogen and (v) high phosphorus and high nitrogen. To reduce zooplankton grazers, 1+ fish (Perca fluviatilis L.) were stocked in all enclosures at a density of 3.7 individuals m−2. 2. With the addition of phosphorus, chlorophyll a and the total biovolume of phytoplankton rose significantly at moderate and high nitrogen. Cyanobacteria or chlorophytes dominated in all enclosures to which we added phosphorus as well as in the high nitrogen treatment, while cryptophytes dominated in the moderate nitrogen enclosures and the controls. 3. At the end of the experiment, the biomass of the submerged macrophytes Elodea canadensis and Potamogeton sp. was significantly lower in the dual treatments (TN, TP) than in single nutrient treatments and controls and the water clarity declined. The shift to a turbid state with low plant coverage occurred at TN >2 mg N L−1 and TP >0.13–0.2 mg P L−1. These results concur with a survey of Danish shallow lakes, showing that high macrophyte coverage occurred only when summer mean TN was below 2 mg N L−1, irrespective of the concentration of TP, which ranged between 0.03 and 1.2 mg P L−1. 4. Zooplankton biomass and the zooplankton : phytoplankton biomass ratio, and probably also the grazing pressure on phytoplankton, remained overall low in all treatments, reflecting the high fish abundance chosen for the experiment. We saw no response to nutrition addition in total zooplankton biomass, indicating that the loss of plants and a shift to the turbid state did not result from changes in zooplankton grazing. Shading by phytoplankton and periphyton was probably the key factor. 5. Nitrogen may play a far more important role than previously appreciated in the loss of submerged macrophytes at increased nutrient loading and for the delay in the re-establishment of the nutrient loading reduction. We cannot yet specify, however, a threshold value for N that would cause a shift to a turbid state as it may vary with fish density and climatic conditions. However, the focus should be widened to use control of both N and P in the restoration of eutrophic shallow lakes.

Atmospheric inputs of phosphorus and nitrogen to the southwest Mediterranean region: Biogeochemical responses of high mountain lakes

Abstract: We quantified dry and wet deposition of dust, nitrogen, and phosphorus over the southwest Mediterranean region (Sierra Nevada, Spain) and assessed its effects on the nutrient status and the chlorophyll a (Chl a) concentration in two high mountain lakes. Atmospheric deposition of particulate matter (PM) and total phosphorus (TP) were mainly associated with dryfall and showed a seasonal pattern similar to that reported for Saharan dust export toward the Mediterranean region, with maxima during spring and summer. In contrast, total nitrogen (TN) deposition was related to rainfall and did not follow the pattern observed for PM and TP. The molar TN : TP ratio was significantly lower (i.e., phosphorus-enriched) in dry deposition (TN vs. TP slope 5 11.2) than in wet deposition (TN vs. TP slope 5 95.5). In the study lakes, the molar TN : TP ratios and the Chl a concentrations were significantly influenced by the molar TN : TP ratio and the TP content of atmospheric deposition, respectively. Lake responses were more pronounced in the more phosphorous-limited system. These results establish a direct connection between atmospheric deposition and lake nutrient status and Chl a, making evident that in the Mediterranean region these inputs are an important source of phosphorous affecting biogeochemistry of oligotrophic systems.

Source, transport and deposition of atmospheric phosphorus over the northwestern mediterranean

Abstract: Atmospheric concentrations and total deposition (wet+dry) of phosphorus were measured over the northwestern Mediterranean between april 1985 and march 1988. A seasonal cycle of both atmospheric concentrations and total deposition is observed, the higher values being recorded during the dry season. Air-mass trajectory analyses allow an identification of the major sources of atmospheric phosphorus: soil-derived dust from desert areas of north Africa and anthropogenic emissions from european countries. The impact of the atmospheric input as a source of phosphorus for surface Mediterranean waters is tentatively assessed on both annual and seasonal time scales. The results suggest that the atmospheric input of phosphorus could be significant to Mediterranean oligotrophic zones, especially during summer when phosphorus input from deeper waters into the photic layer is minimum.

Involvement of Phosphorus in Nitrogen Fixation by Subterranean Clover (Trifolium subterraneum L.)

Abstract: Effects of phosphorus supply on nodulation and nitrogen fixation in subterranean clover paralleled those on growth and occurred only after, or at the same time as, growth responses. However, correcting phosphorus deficiency increased nitrogen concentrations in tops as well as weight of tops. Effects of vesicular-arbuscular (VA) mycorrhizas on growth, nodulation and nitrogen fixation operated through effects on phosphorus nutrition of the host. Inoculation with a VA mycorrhizal fungus only stimulated nodulation and nitrogen fixation when insufficient phosphorus was applied for maximum growth of the non-mycorrhizal plant. Phosphorus concentrations in nodules greatly exceeded those in either tops or roots in both mycorrhizal and non-mycorrhizal plants and with phosphorus levels ranging from severely deficient to luxury supply for plant growth. Nitrogen applied after nitrogen fixation had commenced increased fresh weight of tops to a greater extent where phosphorus was non-limiting to growth. This positive interaction between nitrogen and phosphorus on the growth of nodulated nitrogen-fixing subterranean clover suggests that phosphorus deficiency does not limit growth in legumes by decreasing nitrogen fixation. It is concluded that increasing phosphorus supply increases nitrogen fixation in subterranean clover by stimulating host plant growth rather than by effects on either rhizobial growth and survival or on nodule formation and function.