Does differential iron supply to algae affect Daphnia life history? An ionome-wide study

Heterotrophic denitrification enhancement via effective organic matter degradation driven by suitable iron dosage in sediment

The control of internal pollution was important throughout the restoration of the lake, especially the removal of sediment internal nitrogen. Experiments involving incubation were conducted in this study to investigate the effects of iron remediation on nitrogen in both water and sediment. Adding iron with varying dosage had different effects on the nutrients content and other properties of water and sediment in remediation. The higher the addition dosage of iron, the more iron ions were released into the interstitial and overlying water. The effect of 5% and 10% iron dosage on the interstitial and overlying water were more obvious, which can significantly increase the pH and decrease the ORP of the sediment, and significantly increase the TN and NH4+-N contents in overlying water. Nevertheless, higher iron addition dosage decreased relative abundance of the genera related to denitrification (Thiobacillus) and DNRA (Bacillus). The relative abundance of Anaerolineae was increased with the iron addition dosage, promoted the reduction of organic matter and iron cycle in sediment. The iron addition dosage of 2% had less effect on the overlying water quality, and promoted the nitrogen removal process by changing the abundance of microorganisms related to the sediment nitrogen cycle. This study provides essential information for internal pollution control of lakes and serves as a valuable reference for developing eutrophication management framework.

Spatiotemporal Variation in Dissolved, Bioavailable, and Particulate Elements and the Abundance of Harmful Algae in Grand Lake

Harmful algal blooms (HABs) are often linked to the increased loading of limiting nutrients such as nitrogen and phosphorus. Little is known about the relevance of other biogenic elements, the supplies of which are spatiotemporally heterogeneous, on HABs. We measured the dissolved, bioavailable, and particulate concentrations of 26 elements at four locations draining different catchments of a large reservoir during three seasons, in addition to the total abundance of phytoplankton and % of cyanobacteria. Finally, we manipulated a key element (Fe) in microcosms to test its effect on the community. Phytoplankton abundance and community structure varied spatiotemporally, with minimal variation in N/P. The variation in environmental supplies of several other elements was correlated with phytoplankton abundance, as well as up to 3 orders of magnitude differences in cyanobacterial yield. Bioassays manipulating Fe impacted total phytoplankton as well as the abundance of cyanobacteria, with Fe-chelated treatments resulting in a significant decline in phytoplankton as well as cyanobacterial yield. In summary, we found substantial heterogeneity in elemental supplies that are relevant to the phytoplankton community. Exploring the relevance of the entire system of elements in the context of HABs may be more rewarding than studies emphasizing a subset of elements.

Elemental and biochemical nutrient limitation of zooplankton: A meta-analysis

Primary consumers in aquatic ecosystems are frequently limited by the quality of their food, often expressed as phytoplankton elemental and biochemical composition. However, the effects of these food quality indicators vary across studies, and we lack an integrated understanding of how elemental (e.g. nitrogen, phosphorus) and biochemical (e.g. fatty acid, sterol) limitations interactively influence aquatic food webs. Here, we present the results of a meta-analysis using >100 experimental studies, confirming that limitation by N, P, fatty acids, and sterols all have significant negative effects on zooplankton performance. However, effects varied by grazer response (growth vs. reproduction), specific manipulation, and across taxa. While P limitation had greater effects on zooplankton growth than fatty acids overall, P and fatty acid limitation had equal effects on reproduction. Furthermore, we show that: nutrient co-limitation in zooplankton is strong; effects of essential fatty acid limitation depend on P availability; indirect effects induced by P limitation exceed direct effects of mineral P limitation; and effects of nutrient amendments using laboratory phytoplankton isolates exceed those using natural field communities. Our meta-analysis reconciles contrasting views about the role of various food quality indicators, and their interactions, for zooplankton performance, and provides a mechanistic understanding of trophic transfer in aquatic environments.

Growth and ionomic responses of a freshwater cyanobacterium to supplies of nitrogen and iron

Cyanobacterial harmful algal blooms (HABs) are increasing in frequency and magnitude worldwide. A number of parameters are thought to underlie HABs, including the ratio at which two key elements, nitrogen (N) and phosphorus (P) are supplied, although a predictive understanding eludes us. While the physiological importance of iron (Fe) in electron transport and N-fixation is well known, relatively little is known about its impacts on the growth of freshwater cyanobacteria. Moreover, there is growing appreciation for correlated changes in the quotas of multiple elements encompassing an organism (i.e. the ionome) when the supply of one element changes, indicating that growth differences arise from complex biochemical adjustments rather than limitation of a key anabolic process by a single element. In this study, the effects of supply N:P and Fe on the growth and ionome of Dolichospermum, a nitrogen-fixing cyanobacterium found in freshwater ecosystems, were examined. Changes in both supply N:P and Fe had significant effects on yield. Consistent with prior observations, cyanobacterial growth was higher at N:P = 20, compared to N:P = 5, and quotas of all elements decreased with growth. Yield was negatively related with the degree of imbalance between dissolved supply and intracellular concentrations of not only N and Fe, but also multiple other elements. Changes in Fe supply had a significant effect on yield in N-limited conditions (N:P = 5). Again, ionome-wide imbalances decreased yield. Together, these results indicate that attention to multiple elements encompassing the ionome of a HAB-forming taxon, and the supplies of such elements may help improve the ability to forecast blooms. Such elemental interactions may be critical as limnologists begin to appreciate the staggering variation in the supplies of such elements among lakes, and anthropogenic activities continue to alter global biogeochemical cycles.