Assessing nutrient limitation in a subtropical reservoir

Abstract

There is debate about the relative importance of controlling anthropogenic nitrogen (N) versus phosphorus (P) inputs to limit algal growth in lakes and reservoirs. Our study examined nutrient responses in a subtropical reservoir using short-term algal bioassays on 3 occasions, once during the austral winter and twice during the austral summer. Measurement of photosynthetic yield (Fv/Fm) was used to determine the response to nutrient addition. For the 2 summer sampling occasions, the photosynthetic yields of the N+P treatments were significantly higher than the control. At some sites and on some occasions there was a response to P or N alone, but there was no consistent pattern. The one winter sampling occasion had no response to nutrient addition. Overall, the magnitude of the photosynthetic yield of algal samples correlated with nitrate/nitrite (NO 2 − /NO 3 − ) and soluble reactive phosphorus (SRP) concentrations, but not with ammonium (NH 4 + ), or dissolved organic N (DON) or P (DOP), despite relatively high concentrations of DON. Therefore we concluded that both N and P co-limited the growth of phytoplankton in the 2 austral summer sampling occasions. This contrasted with high N:P ratios and low P concentrations observed, which suggested that the reservoir was most likely to be P limited. This study highlights the importance of determining algal responses to nutrients and measures nutrient concentrations and ratios to determine whether N or P should be controlled to prevent algal blooms.

Punching above their weight: Large release of greenhouse gases from small agricultural dams

“…Interestingly and contrary to our hypothesis, we found no relationship between phosphate concentrations and CO 2 or CH 4 emissions, albeit being widely accepted that freshwater phytoplankton communities are predominantly phosphorous limited (Hecky & Kilham, ; Schindler et al., ). Multiple‐nutrient limitations on phytoplankton have, however, been demonstrated in freshwater systems (Muhid & Burford, ; Smith et al., ), largely attributed to species‐specific variation in optimum nutrient ratios for growth (Hecky & Kilham, ), which may also be co‐limited by physical factors such as temperature and light (Healey, ; Hecky & Kilham, ). More research is needed to quantify the mechanisms behind farm dam GHG emissions and phosphate concentration incongruence.…”

The Impact of Nitrogen and Phosphorus Dynamics on the Kinneret Phytoplankton: II: Chlorophyta, Cyanophyta, Diatoms and Peridinium

“…The events sequence is briefed as follows: Climate changes, temperature increase [21], and precipitation reduction as well as Jordan River discharge decline together with nitrogen removal in the drainage basin yielding lowered lake water level and nitrogen inputs. It also results in nitrogen decline and limitation for Peridinium and consequently decline of phosphorus fluxes into the Epilimnion through Cysts mediated phosphorus [22]. In addition, it results in Chlorophyta, Cyanophyta and diatoms growth rates enhancement partly as a result of absence of competition with Peridinium.…”

Science to Support Management of Receiving Waters in an Event-Driven Ecosystem: From Land to River to Sea

“…For example, trajectories of increasing phytoplankton biomass (chlorophyll a concentration) and abundance have been observed over time [24]. Research has also shown that while phytoplankton growth in the reservoirs is limited by both nitrogen and phosphorus [25,26], phosphorus additions can lead to preferential growth enhancement of Cylindrospermopsis raciborskii, a dominant toxic cyanobacteria in the reservoirs [27]. Together, these findings suggest that water quality is likely to continue to deteriorate if nutrient loads from catchments are not mitigated, and that effective management will require mitigation measures that target both nitrogen and phosphorus.…”

“…Reducing loads of nitrogen and phosphorus from catchments [25,26,69] Taste and odour compounds Reducing loads of nitrogen and phosphorus from catchments [70] Poor water quality Best land management practices; Reducing loads of nutrients and sediment from catchments [21,23,31] [19,68] Macroinvertebrate and native fish diversity decline…”

“…Reducing loads of nitrogen and phosphorus from catchments [25,26,69] Taste and odour compounds Reducing loads of nitrogen and phosphorus from catchments [70] Poor water quality…”