Evidence for extensive but variable nutrient limitation in New Zealand lakes

Large greenhouse gases emissions from China's lakes and reservoirs

Freshwaters are important sources of greenhouse gases (GHGs) to the atmosphere that may partially offset the terrestrial carbon sink. However, current emission estimates from inland waters remain uncertain due to data paucity in key regions with a large freshwater surface area, such as China. Here, we show that the areal fluxes of GHGs (carbon dioxide, methane, and nitrous oxide) from lakes and reservoirs in China are much larger than previous estimates. Our work summarized data from 310 lakes and 153 reservoirs, and revealed diffusive emissions of 1.56 (95% confidence interval: 1.12-2.00) Tg C-CH₄/y and 25.2 (20.8-29.5) Tg C-CO₂/y from reservoirs and lakes. Chinese lakes and reservoirs emit 175.0 (134.7-215.3) Tg CO₂ equivalent, with 73.4% of this forcing contributed by lakes. These aquatic sources are equivalent to 14.1%-22.6% of China's estimated terrestrial carbon sink. Our results suggest a disproportionally high contribution of China's reservoirs and lakes to national and global GHGs emissions, highlighting major data gaps and the need of including more artificial and natural lakes data from developing countries like China in global GHGs budgets.

Phosphorus availability in the source population influences response to dietary phosphorus quantity in a New Zealand freshwater snail

We investigated whether previously documented variation among populations in availability of dietary phosphorus (P) is linked to heterogeneity in growth rate of the New Zealand freshwater snail Potamopyrgus antipodarum on a P-limited diet. We chose this system because P. antipodarum inhabits water bodies that vary in P availability and because P. antipodarum growth rate varies considerably in response to low P. We quantified specific growth rate and alkaline phosphatase (AP) expression in a diverse array of juvenile P. antipodarum fed high vs. low-P diets. We found strong associations between P content of epilithon in the source lake and P. antipodarum growth rate on high vs. low-P diets, with snails collected from lakes with relatively low-P epilithon showing the greatest increase in growth rate on the high-P relative to low-P diet. We also found substantial intraspecific variation in growth response to P limitation. Expression of AP also varied among lineages and was negatively associated with C: P of lake epilithon but did not explain the relationship between C: P in the lake of origin and sensitivity to P limitation. Together, our results demonstrate a strong signature of the P environment in the lake of origin on how this snail responds to P limitation as well as preliminary evidence for intraspecific variation of AP expression in animals.