Earlier winter/spring runoff and snowmelt during warmer winters lead to lower summer chlorophyll‐a in north temperate lakes. (20th July 2021)

• Record Type: Journal Article
• Authors: Hrycik, Allison R.; Isles, Peter D. F.; Adrian, Rita; Albright, Matthew; Bacon, Linda C.; Berger, Stella A.; Bhattacharya, Ruchi; Grossart, Hans‐Peter; Hejzlar, Josef; Hetherington, Amy Lee; Knoll, Lesley B.; Laas, Alo; McDonald, Cory P.; Merrell, Kellie; Nejstgaard, Jens C.; Nelson, Kirsten; Nõges, Peeter; Paterson, Andrew M.; Pilla, Rachel M.; Robertson, Dale M.; Rudstam, Lars G.; Rusak, James A.; Sadro, Steven; Silow, Eugene A.; Stockwell, Jason D.; Yao, Huaxia; Yokota, Kiyoko; Pierson, Donald C.
• Is Part Of: Global change biology. Volume 27:Number 19(2021)
• Page Start: 4615
• Page End: 4629
• Publication Date: 2021-07-20
• Subjects: chlorophyll‐a -- climate change -- long‐term data -- phytoplankton biomass -- snowmelt -- stream discharge; Climatic changes -- Environmental aspects -- Periodicals; Troposphere -- Environmental aspects -- Periodicals; Biodiversity conservation -- Periodicals; Eutrophication -- Periodicals; 551.5
• DOI: 10.1111/gcb.15797
• Languages: English
• ISSNs: 1354-1013

Abstract

Abstract: Winter conditions, such as ice cover and snow accumulation, are changing rapidly at northern latitudes and can have important implications for lake processes. For example, snowmelt in the watershed—a defining feature of lake hydrology because it delivers a large portion of annual nutrient inputs—is becoming earlier. Consequently, earlier and a shorter duration of snowmelt are expected to affect annual phytoplankton biomass. To test this hypothesis, we developed an index of runoff timing based on the date when 50% of cumulative runoff between January 1 and May 31 had occurred. The runoff index was computed using stream discharge for inflows, outflows, or for flows from nearby streams for 41 lakes in Europe and North America. The runoff index was then compared with summer chlorophyll‐ a (Chl‐ a ) concentration (a proxy for phytoplankton biomass) across 5–53 years for each lake. Earlier runoff generally corresponded to lower summer Chl‐ a . Furthermore, years with earlier runoff also had lower winter/spring runoff magnitude, more protracted runoff, and earlier ice‐out. We examined several lake characteristics that may regulate the strength of the relationship between runoff timing and summer Chl‐ a concentrations; however, our tested covariates had little effect on the relationship. Date of ice‐out was not clearly related to summer Chl‐ a concentrations. Our results indicate that ongoing changes in winter conditions may have important consequences for summer phytoplankton biomass and production. Abstract : Summer chlorophyll‐ a (Chl‐ a ) in north temperate lakes has a positive relationship with winter–spring runoff timing (a), indicating that years with early runoff have lower summer Chl‐ a . Summer Chl‐ a is also positively related to the volume of winter–spring runoff (b), that is, years with high stream discharge volume have higher Chl‐ a . Duration of winter–spring runoff is negatively related to runoff timing (c), and runoff timing is positively related to runoff volume (d), indicating that years with early runoff also have more protracted runoff and lower stream discharge volume.