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Evidence suggests that low cobalt (Co) may limit heterocyst frequency (HF) in filamentous diazotrophic cyanobacteria. Therefore, the effect of three Co concentrations on HF in four species in the genera Aphanizomenon and Dolichospermum was examined in N‐depleted (N was not added) culture. Long‐term HF data were also analysed in experimentally fertilised N‐limited Lake 227.HF ranges and means at 0.17, 17, and 170 nmol Co/L were 4.1%–5.7% (4.6%), 5.4%–7.4% (6.4%), and 5.9%–9.3% (7.4%), respectively, after 11 days of growth in batch cultures suggesting that Co plays a role in regulating HF. HF at 0.17 nmol/L was significantly different from HF at the two higher concentrations in all species implicating Co in heterocyst differentiation. However, growth rates and final biovolume yields were not significantly affected by Co in any of the species.Applying the ratio of total phosphorus (TP)/Co in culture media (106) at 0.17 nmol Co/L to an N‐limited system implies that dissolved Co would have to be less than 1 pmol/L to severely limit HF at 1 μmol TP/L. This Co concentration is much lower than dissolved Co in Lake 227 during an Aphanizomenon skujae bloom with 1 μmol TP/L in 2017. Furthermore, Co increased from 0.7 to 2.0 nmol/L simultaneously increasing with HF and cyanobacteria biomass suggesting that Co probably did not limit HF and bloom biomass in Lake 227.Mean summer HFs in Lake 227 during 2000–2020 were 3.4% (epilimnion) and 4.0% (metalimnion), similar to HF at the lowest Co in the cultures. However, HF was significantly higher after 2015 following a shift in dominant bloom species from A. schindlerii to the smaller A. skujae. Calculations suggest that the decrease in cell size may have prompted a higher HF in A. skujae in order to fix an amount of N per unit biomass similar to that fixed by the larger A. schindlerii. Thus, two previously unidentified factors, Co and cell size, can be added to the list of factors that affect HF. [ABSTRACT FROM AUTHOR]

Citizen science projects have a long history in ecological studies. The research usefulness of such projects is dependent on applying simple and standardized methods. Here, we conducted a citizen science project that involved more than 3500 Swedish high school students to examine the temperature difference between surface water and the overlying air (Tw-Ta) as a proxy for sensible heat flux (QH). If QH is directed upward, corresponding to positive Tw-Ta, it can enhance CO2 and CH4 emissions from inland waters, thereby contributing to increased greenhouse gas concentrations in the atmosphere. The students found mostly negative Tw-Ta across small ponds, lakes, streams/rivers and the sea shore (i.e. downward QH), with Tw-Ta becoming increasingly negative with increasing Ta. Further examination of Tw-Ta using high-frequency temperature data from inland waters across the globe confirmed that Tw-Ta is linearly related to Ta. Using the longest available high-frequency temperature time series from Lake Erken, Sweden, we found a rapid increase in the occasions of negative Tw-Ta with increasing annual mean Ta since 1989. From these results, we can expect that ongoing and projected global warming will result in increasingly negative Tw-Ta, thereby reducing CO2 and CH4 transfer velocities from inland waters into the atmosphere.

Hydrologic management of shallow lakes is often undertaken to prevent fluctuations in lake level, and to ensure sufficient water volume for economic, domestic, and recreational uses, but there is inconsistent evidence of whether lake‐level stabilisation through hydrological management promotes or hinders eutrophication.Here we used multi‐proxy paleolimnological assessments of water quality (sedimentary carbon, nitrogen, total phosphorus, fossil pigments), and zooplankton community ecology (fossil Cladocera assemblages), combined with Landsat‐derived estimates of lake surface area in two shallow eutrophic lakes, in the Prairies of southern Saskatchewan, Canada, to quantify how 8 decades of contrasting hydrological management strategies (continuous or intermittent) affect primary production and phytoplankton composition.Analysis revealed that irregular hydrological management of Pelican Lake led to sharp increases in primary production concomitant with lake‐level decline. In contrast, continuously managed Buffalo Pound Lake, a drinking water reservoir for regional cities, exhibited slow, persistent eutrophication over decades despite active regulation of water levels. In both lakes, strong correlations of δ 15N values with pigments from diazotrophic cyanobacteria (canthaxanthin) showed that N2‐fixation increased during eutrophication irrespective of the timing of change. Finally, variation in fossil cladoceran density and composition reflected changes in pelagic and littoral habitats (e.g., reduced macrophyte cover) due to changes in both lake level and water quality.Basin comparison shows that while hydrologic management can moderate water quality degradation due to lake‐level change, it does not prevent eutrophication when nutrient influx remains high.Given that regional water availability is forecast to decline in coming decades, we anticipate that continued hydrological management will be unavoidable and will be unable to improve water quality unless nutrient influx is also controlled. [ABSTRACT FROM AUTHOR]

Many physical, chemical, and biological processes in freshwater ecosystems mobilize the nutrient phosphorus (P) from sediments, which in turn may contribute to the formation of harmful algal blooms. Here, we critically reviewed internal P loading in Canadian fresh waters to understand the geographic patterns and environmental drivers of this important process. From 43 publications, we consolidated 618 estimates of internal P loading from Canadian freshwater ponds, lakes, reservoirs, and coastal wetlands (n = 70). Expressed in terms of total P, short-term gross rates in sediment samples ([L.sub.gross]) ranged from -27 to 54 mg x [m.sup.-2] x [day.sup.-1] (n = 461), while long-term net rates in whole ecosystems ([L.sub.net]) ranged from -1694 to 10 640 mg x [m.sup.-2] x [year.sup.-1] (n = 157). The main environmental drivers of this variation were oxygen, pH, geology, and trophic state. Internal P loading tended to be higher during the open-water season and most prominent in small prairie lakes. Priorities for future research on internal P loading should include resolving methodological problems, assessing the relative importance of different mechanisms, examining the influence of anthropogenic activities, and quantifying rates in understudied ecosystems. Resume : De nombreux processus physiques, chimiques et biologiques dans les ecosystemes d'eau douce mobilisent le phosphore (P), un element nutritif, des sediments, ce qui peut favoriser la formation de fleurs d'eau nefastes. Nous avons effectue un examen critique de l'apport interne de P dans les plans d'eau douce canadiens afin de comprendre les motifs de repartition geographique et les facteurs environnementaux qui influent sur cet important processus. A la lumiere de 43 publications, nous avons collige 618 estimations de l'apport interne de P d'etangs, de lacs, de reservoirs et de milieux humides littoraux d'eau douce canadiens (n = 70). Exprimes en termes de P total, les taux d'apport de P a court terme pour les echantillons de sediments ([L.sub.gross]) vont de -27 a 54 mg x [m.sup.-2] x [jour.sup.-1] (n = 461), alors que les taux nets a long terme a l'echelle de l'ecosysteme ([L.sub.net]) vont de -1694 a 10 640 mg x [m.sup.-2] x [an.sup.-1] (n = 157). Les principaux facteurs environnementaux influant sur ces variations sont l'oxygene, le pH, la geologie et l'etat trophique. L'apport interne de P tend a etre plus eleve durant la periode d'eau libre et le plus marque dans les petits lacs de prairie. La priorite des travaux futurs sur l'apport interne de P devrait porter sur la resolution de problemes methodologiques, l'evaluation de l'importance relative de differents mecanismes, l'examen de l'influence des activites humaines et la quantification des taux dans les ecosystemes sous-etudies. [Traduit par la Redaction], Introduction Globally, eutrophication is one of the key drivers of change in aquatic ecosystems (Millenium Ecosystem Assessment 2005). Eutrophication causes poor water clarity, oxygen depletion, fish kills, and biodiversity loss, [...]

Globally, hydrological connectivity between rivers and their floodplains has been reduced by river flow management and land transformation. The Saskatchewan River Delta is North America's largest inland delta and a hub for fish and fur production. To determine the influence of connectivity on limnology within this northern floodplain, water chemistry and stable isotopes (δ][sup.18]O and δ²H) were analyzed during the winter of 2014 in 26 shallow lakes along a hydrological gradient. A total of five lake connectivity categories were determined by optical remote sensing imagary of surface water coverage area from years of varying flood intensities. Accuracy of categories was verified by degree of [sup.18]O and ²H enrichment within lakes. Both isotopes showed marked successional enrichment between connectivity categories, with more isolated lakes exhibiting greater enrichment. Water chemistry in lakes with greater connectivity to the main channel were characterized by higher pH, dissolved oxygen, nitrates, and sulfates and lower total nitrogen, total phosphorus, and ammonium compared with more isolated lakes. These findings illustrate how connectivity influences water chemistry in northern floodplain lakes and how it might determine the suitability of these lakes as winter refuge for fishes. Additionally, our study provides supporting evidence for the effective use of optical remote sensing imagery, an inexpensive and accessible source of data for researchers, when determining connectivity characteristics of large northern floodplain systems. Additionally, this study provides further evidence that the inundation of floodplain lakes by river water during peak discharge has an impact on the conditions within the lakes long into the winter ice-cover season. Understanding the year-round influence of river-floodplain connection is imperative for assessing potential impacts of climate change and future water regulation on such ecosystems. A l'echelle planetaire, la gestion des debits des rivieres et la transformation du territoire ont entraine une diminution de la connectivite hydrologique entre les rivieres et les plaines inondables. Le delta de la riviere Saskatchewan est le plus grand delta interieur d'Amerique du Nord et une plaque tournante pour la production de poissons et de fourrures. Afin de determiner l'influence de la connectivite sur la limnologie dans cette plaine inondable septentrionale, la chimie de l'eau et ses isotopes stables (δ[sup.18]O et δ²H) ont ete analyses durant l'hiver 2014 dans 26 lacs peu profonds le long d'un gradient hydrologique. Cinq categories de connectivite des lacs ont ete etablies au total sur la base d'images optiques de teledetection des aires recouvertes par les eaux de surface pour des annees caracterisees par differentes intensites des crues. L'exactitude des categories a ete verifiee a la lumiere du degre d'enrichissement en [sup.18]O et ²H dans les lacs. Les deux isotopes presentaient un enrichissement progressif marque entre les categories de connectivite, les lacs plus isoles montrant un enrichissement plus important. La chimie de l'eau dans les lacs de plus grande connectivite au chenal principal etait caracterisee par un pH et des concentrations d'oxygene dissous, de nitrates et de sulfates plus eleves et des concentrations d'azote total, de phosphore total et d'ammonium plus faibles comparativement aux lacs plus isoles. Ces resultats illustrent l'influence de la connectivite sur la chimie de l'eau dans les lacs de plaines inondables septentrionales et comment elle pourrait determiner l'adequation de ces lacs comme refuges hivernaux pour les poissons. En outre, notre etude fournit des donnees temoignant de l'utilite de l'imagerie optique de teledetection, une source de donnees accessible et peu couteuse, pour la determination des caracteristiques de connectivite des grands systemes de plaines inondables nordiques. L'etude fournit aussi de nouvelles donnees appuyant la these voulant que l'inondation des lacs de plaines inondables par l'eau de riviere en periode de debits de pointe ait une incidence persistante sur les conditions dans les lacs durant la periode hivernale de couverture de glace. La comprehension de l'influence tout au long de l'annee de la connexion riviereplaine inondable est necessaire a l'evaluation des impacts potentiels des changements climatiques et de la regularisation future de l'eau sur de tels ecosystemes. [Traduit par la Redaction], Introduction Floodplains are among the most productive and threatened ecosystems on earth. As a result of anthropogenic river flow management and land transformation, 90% of floodplains within North America have [...]

Inland waters are hotspots of greenhouse gas (GHG) cycling, with small water bodies particularly active in the production and consumption of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). However, wetland ponds are being replaced rapidly by small constructed reservoirs in agricultural regions, yet it is unclear whether these two water body types exhibit similar physical, chemical, and environmental controls of GHG content and fluxes. Here, we compared the content and regulatory mechanisms of all three major GHGs in 20 pairs of natural wetland ponds and constructed reservoirs in Canada's largest agricultural region. Carbon dioxide content was associated primarily with metabolic indicators in both water body types; however, primary production was paramount in reservoirs, and heterotrophic metabolism a stronger correlate in wetland ponds. Methane concentrations were correlated positively with eutrophication of the reservoirs alone, while competitive inhibition by sulfur‐reducing bacteria may have limited CH4 in both waterbody types. Contrary to expectations, N2O was undersaturated in both water body types, with wetlands being a significantly stronger and more widespread N2O sink. Varying regulatory processes are attributed to differences in age, depth, morphology, and water‐column circulation between water body types. These results suggest that natural and constructed water bodies should be modeled separately in regional GHG budgets. Plain Language Summary: Small inland water bodies, ponds and reservoirs, are hotspots of greenhouse gas (GHG) production. However, modern farming practices replace natural wetlands by artificial reservoirs, without consideration on the effects on landscape GHG fluxes. Here we measured concentrations and controls of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in locally‐paired wetland ponds and agricultural reservoirs and found that while GHG concentrations were similar in the two waterbody types, underlying mechanisms differed, owing to the differences in shape, depth, and age of individual water bodies. Shallower wetland ponds were typically more fully mixed, exhibited more oxygen at depth, and had higher nutrients and organic carbon concentrations reflecting their ages. Findings suggest that the balance between wetland drainage and reservoir construction may have a pronounced effect on regional budgets of GHG fluxes, particularly in the face of forthcoming climate changes. Key Points: CO2 content was associated with metabolism; primary production in reservoirs, but bacterial respiration in wetlandsCH4 concentrations were correlated positively with either eutrophication (reservoirs) or competitive inhibition of methanogenesis (both)N2O undersaturation was ubiquitous, but wetlands were stronger and more widespread N2O sinks [ABSTRACT FROM AUTHOR]

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