Coherent response of lakes in Ontario, Canada to reductions in sulphur deposition: the effects of climate on sulphate concentrations

International audienceSulphate deposition in south-central Ontario declined between 1976 and 2000 by more than 50%, whereas lake sulphate (SO42?) concentrations decreased by, on average, only half as much. To investigate the factors that controlled this slower than expected response, the temporal patterns in lake SO42? concentrations were compared with patterns in both deposition and climate, since climate has a major influence on the hydrological cycle in this part of the continent. To do this, the temporal coherence in SO42? concentrations between 9 lake basins was estimated using the intraclass correlation from a repeated-measures analysis of variance and two subsets of lakes were found (six in one group, four in the other), each with lakes having synchronous patterns. One subset (4 lakes) included the 3 with the longest water replenishment times (>3.4 yr) which are expected to respond to decreases in SO42? deposition more slowly. However, the average pattern reflecting the temporal changes of each of the two subsets was very similar. The response of both subsets of lakes to the decreasing SO42? deposition over two decades was independent of the degree of acidification or sensitivity to acidification of the lakes. In a determination of which factors best predicted each of those two subsets' SO42? time series, good predictive models were produced by regional/global-scale climate indices, specifically the Southern Oscillation Index (SOI) describing the El Niño Southern Oscillation (ENSO) and the North Atlantic Oscillation Index (NAOI), as well as by SO42? deposition indices. When the predictor variables were combined, models which described the long-term changes in lake SO42? concentration best included the SOI, the NAOI and SO42? deposition. Thus, large-scale climate factors play a major role in determining the response of aquatic systems to changes in SO42? deposition, perhaps through their influence on lake and/or catchment processes that effectively delay recovery. Keywords: Atmospheric deposition, lake recovery, temporal trends, climate, temporal coherenc

Nitrogen and phosphorus loads to temperate seepage lakes associated with allochthonous dissolved organic carbon loads

Terrestrial loads of dissolved organic matter (DOM) have increased in recent years in many north temperate lakes. While much of the focus on the “browning” phenomena has been on its consequences for carbon cycling, much less is known about how it influences nutrient loading to lakes. We characterize potential loads of nitrogen and phosphorus to seepage lakes in northern Wisconsin, USA, based on a laboratory soil leaching experiment and a model that includes landscape cover and watershed area. In these seepage lakes, nutrient concentrations are positively correlated with dissolved organic carbon concentrations (nitrogen: r = 0.68, phosphorus: r = 0.54). Using long‐term records of browning, we found that dissolved organic matter‐associated nutrient loadings may have resulted in substantial increases in nitrogen and phosphorus in seepage lakes and could account for currently observed nutrient concentrations in the lake. “Silent” nutrient loadings to brown‐water lakes may lead to future water‐quality concerns. PLAIN LANGUAGE SUMMARY: The color of many temperate lakes is changing; some lakes are becoming more darkly stained brown. The tea‐colored stain is due to dissolved organic matter from the surrounding landscape. Much of the research related to the causes and consequences of increased staining, or “brownification,” relate to its connection to the carbon cycle. However, by examining long‐term lake chemical records, analyzing the properties of the organic compounds, and modeling potential flows of the compounds, we find that carbon is not the only element that is influenced by browning. Nitrogen and phosphorus, two nutrients important to growth of organisms at the base of the food web, may also be increasing in lakes due to brownification."Funding for this research was supported by the Northern Research Station and the Chequamegon-Nicolet National Forest (CNNF) of the United States Department of Agriculture (USDA) Forest Service and a National Science Foundation (NSF) grant to the University of Wisconsin-Madison to support the North Temperate Lakes Long-Term Ecological Research (NTLLTER) Site (DEB-#1440297)."https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL07721

The role of wetland coverage within the near-stream zone in predicting of seasonal stream export chemistry from forested headwater catchments

Postprint version. "This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record."Stream chemistry is often used to infer catchment‐scale biogeochemical processes. However, biogeochemical cycling in the near‐stream zone or hydrologically‐connected areas may exert a stronger influence on stream chemistry compared with cycling processes occurring in more distal parts of the catchment, particularly in dry seasons and in dry years. In this study, we tested the hypotheses that near‐stream wetland proportion is a better predictor of seasonal (winter, spring, summer and fall) stream chemistry compared with whole‐catchment averages and that these relationships are stronger in dryer periods with lower hydrologic connectivity. We evaluated relationships between catchment wetland proportion and 16‐year average seasonal flow‐weighted concentrations of both biogeochemically‐active nutrients, dissolved organic carbon (DOC), nitrate (NO3‐N), total phosphorus (TP), as well as weathering products, calcium (Ca), magnesium (Mg), at ten headwater (< 200 ha) forested catchments in south‐central Ontario, Canada. Wetland proportion across the entire catchment was the best predictor of DOC and TP in all seasons and years, whereas predictions of NO3‐N concentrations improved when only the proportion of wetland within the near‐stream zone was considered. This was particularly the case during dry years and dry seasons such as summer. In contrast, Ca and Mg showed no relationship with catchment wetland proportion at any scale or in any season. In forested headwater catchments, variable hydrologic connectivity of source areas to streams alters the role of the near‐stream zone environment, particularly during dry periods. The results also suggest that extent of riparian zone control may vary under changing patterns of hydrological connectivity. Predictions of biogeochemically‐active nutrients, particularly NO3‐N, can be improved by including near‐stream zone catchment morphology in landscape models.Funding for this project was provided by a Natural Sciences and Engineering Research Council of Canada Discovery Grant to MCE.https://onlinelibrary.wiley.com/doi/abs/10.1002/hyp.1341

Effects of varicocele treatment in adolescents: A randomized study

Objective: To study the effects of varicocele treatment on testicular function in adolescents. Design: A prospective controlled study in 88 randomly selected adolescents. Setting: All participants were referred to the fertility outpatient clinic of our university hospital. Participants: All participants with a varicocele were randomly assigned into two groups. Group 1 (n = 33) was not treated, whereas group 2 (n = 34) was treated. A similar group of healthy volunteers without a varicocele served as a control group (group 3, n = 21). Interventions: Testes volumes were measured at intake and during follow-up using an orchiometer. Semen analysis was performed according to standard procedures both at intake and after 1 year of follow-up. Serum hormone levels were determined at intake using a radioimmunoassay. Treatment was performed by means of transcatheter embolization of the left testicular vein. Main Outcome Measures: Testes volumes and semen quality at intake and after 1 year of follow-up were compared within and between the three groups. Hormonal parameters were determined at intake only. Results: Before treatment, the mean left testis volume in groups 1 (n = 26) and 2 (n = 27) (20.0 mL; 95% confidence interval [CI]: 18.2 to 21.8 and 21.6 mL; 95% CI: 19.4 to 23.8, respectively) were significantly smaller than those in the control group (n = 19) (24.5 mL; 95% CI: 22.7 to 26.4). During follow-up, left testis volumes of the treated group were comparable with those in the control group (24.2 mL; 95% CI: 22.2 to 26.1 and 24.8 mL; 95% CI: 23.0 to 26.7 respectively) and significantly (P < 0.001) different from the untreated group (20.3 mL; 95% CI: 18.8 to 21.8). A significant increase in left (P < 0.01) as well as right (P < 0.05) testis volume was observed after treatment. Semen parameters before treatment were not significantly different between the three groups. Sperm concentration increased significantly (P < 0.01) from 47.4 x 106/mL (95% CI: 42.5 to 53.3) to 68.9 x 106/mL (95% CI: 50.6 to 87.2) in the treated group, whereas semen quality in the untreated and control groups did not change. Although both testes volumes and sperm concentration improved in the treated group, these phenomena were not consistently correlated to each other. Conclusions: Although not apparent in all adolescents, varicocele correction resulted in an increase in left testis volume and sperm concentration. At this moment, it is not clear if early preventive treatment of varicocele in adolescents, in time, will have a positive effect on testicular function