A qPCR method to quantify bioavailable phosphorus using indigenous aquatic species

Regulating phytoplankton-available suspended particulate phosphorus (P) to control internal P pollution in lake: Conclusion from a short review

The necessity on controlling internal P pollution has been widely reported for lake restoration; thus far, cutting the migrations of soluble P from sediment to overlying water, especially under anoxic condition, is the main target of the internal P pollution control to achieve favorable ecological responses in lake. Here, according to the types of P directly available by phytoplankton, phytoplankton-available suspended particulate P (SPP) pollution, which mainly occurs under aerobic condition and due to sediment resuspension and soluble P adsorption by suspended particle, is found to be the other kind of internal P pollution. The SPP has long been a key index for environmental quality assessment, which could be indirectly reflected by the developed various methods for phytoplankton-available P pool analysis; also, the P has been demonstrated to be a major cause of phytoplankton breeding, typically in shallow lakes. Importantly, compared to the soluble P, SPP pollution clearly has more complicated loading pathways and P activation mechanisms and involves in different fractions of P, even part of which are with relatively high stability in sediment and suspended particle, leading to the potential control measures for the pollution being more complex. Considering the potential differences of internal P pollution among various lakes, this study is therefore calling for more research to focus on regulating phytoplankton-available SPP pollution. Recommendations are also offered to bridge knowledge gap of the regulation to design proper measures for lake restoration.

Schindler's legacy: from eutrophic lakes to the phosphorus utilization strategies of cyanobacteria

David Schindler and his colleagues pioneered studies in the 1970s on the role of phosphorus in stimulating cyanobacterial blooms in North American lakes. Our understanding of the nuances of phosphorus utilization by cyanobacteria has evolved since that time. We review the phosphorus utilization strategies used by cyanobacteria, such as use of organic forms, alternation between passive and active uptake, and luxury storage. While many aspects of physiological responses to phosphorus of cyanobacteria have been measured, our understanding of the critical processes that drive species diversity, adaptation and competition remains limited. We identify persistent critical knowledge gaps, particularly on the adaptation of cyanobacteria to low nutrient concentrations. We propose that traditional discipline-specific studies be adapted and expanded to encompass innovative new methodologies and take advantage of interdisciplinary opportunities among physiologists, molecular biologists, and modellers, to advance our understanding and prediction of toxic cyanobacteria, and ultimately to mitigate the occurrence of blooms.

Characterizing bioavailable phosphorus concentrations in an agricultural stream during hydrologic and streambed disturbances

In freshwater ecosystems, phosphorus (P) is often considered a growth-limiting nutrient. The use of fertilizers on agricultural fields has led to runoff-driven increases in P availability in streams, and the subsequent eutrophication of downstream ecosystems. Isolated storms and periodic streambed dredging are examples of two common disturbances that contribute dissolved and particulate P to agricultural streams, which can be quantified as soluble reactive P (SRP) using the molybdate-blue method on filtered water samples, or total P (TP) measured using digestions on unfiltered water reflecting all forms of P. While SRP is often considered an approximation of bioavailable P (BAP), research has shown that this is not always the case. Current methods used to estimate BAP do not account for the role of biology (e.g., NaOH extractions) or require specialized platforms (e.g., algal bioassays). Here, in addition to routine analysis of SRP and TP, we used a novel yeast-based bioassay with unfiltered sample water to estimate BAP concentrations during two storms (top 80% and > 95% flow quantiles), and downstream of a reach where management-associated dredging disturbed the streambed. We found that the BAP concentrations were often greater than SRP, suggesting that SRP is not fully representative of P bioavailability. The SRP concentrations were similarly elevated during the two storms, but remained consistently low during streambed disturbance. In contrast, turbidity and TP were elevated during all events. The BAP concentrations were significantly related to turbidity during all disturbance events, but with TP only during storms. The novel yeast assay suggests that BAP export can exceed SRP, particularly when streams are not in equilibrium, such as the rising limb of storms or during active dredging.

Formation mechanism of the Microcystis aeruginosa bloom in the water with low dissolved phosphorus

The utilization of phosphorus by algae in the low-phosphorus state has drawn wide concerns due to the high risk of forming algal blooms. The cyanobacteria Microcystis aeruginosa (M. aeruginosa) grew well under low-phosphorus condition by hydrolyzing dissolved organic phosphorus (DOP) to dissolved inorganic phosphorus (DIP) through alkaline phosphatase (AP). There was a negative correlation between DIP concentration and AP activity of algae. AP activity significantly increased at 0-3 d (p < 0.05), and reached the peak values of 43.06 and 49.11 King unit/gprot on day 5 for DIP (0.1 mg/L) and DOP (4.0 mg/L), respectively. The relative expression of phosphate transporter gene increased with decreasing phosphorus concentrations. The catalase activity under low-phosphorus condition increased significantly (p < 0.05) after one week, and was generally higher than 0.15 U/mgprot on day 14. Understanding the utilization efficiency and mechanism of DIP and DOP in the low-phosphorus state would help to inhibit the formation of algal blooms.