Abstract
AbstractThe balance between the availability of energy and nutrients is decisive for the growth and survival of organisms. Here, we evaluated how energy, in this study expressed as total carbon (TC), is lost along the land to ocean aquatic continuum (LOAC) in relation to nutrients, i.e., total phosphorus (TP), total nitrogen (TN), total iron (TFe), and dissolved silica (DSi). For the evaluation, we used data from 4774 lakes, 149 streams, and 52 river mouths from the boreal region. We found that the loss of all chemical variables followed a first order decay function along the LOAC with shortest half‐lives for TFe and DSi (410 d and 568 d, respectively). The half‐life of TC was more than twice as long as for TFe and DSi, resulting in rapidly increasing TC:TFe and TC:DSi ratios along the LOAC. In contrast, TC:TP and TC:TN ratios decreased along the LOAC. The TC and TFe concentration declines along the LOAC were quantitatively similar to the TC and TFe concentration declines from winter to summer, indicating that similar drivers are responsible for spatial and seasonal TC and TFe losses in inland waters. We conclude that the energy:nutrient ratio rapidly changes along the LOAC with an increasing surplus of energy in relation to TFe and DSi the longer water stays in the landscape. These findings have implications for the growth of aquatic organisms along the LOAC, where organisms are likely to become increasingly iron and silica limited with increasing water retention in the landscape.
Highlights
The balance between the availability of energy and nutrients is decisive for the growth and survival of organisms
Catchment and climate drivers of carbon and nutrient concentrations in boreal waters Using data from the 4975 boreal inland waters and applying partial least squares (PLS) regression models, we found that long-term site-specific median concentrations of all chemical variables, i.e., total carbon (TC), total organic carbon (TOC), dissolved inorganic carbon (DIC), total phosphorus (TP), total nitrogen (TN), TFe, and dissolved silica (DSi) showed a dependency on temperature region, site-specific number of growing degree days, and altitude (Table 1)
We further found that the percentage of coniferous forest and open water in the CA was important for TOC, TFe, and DSi concentrations in boreal inland waters but not for DIC, TP, and TN concentrations
Summary
The balance between the availability of energy and nutrients is decisive for the growth and survival of organisms. There are, still some unknowns, one of them being knowledge on how stable the energy:nutrient ratio is when water travels through a lake-rich landscape, i.e., along the land to ocean aquatic continuum (LOAC) of the boreal region This knowledge gap makes predictions of the survival of aquatic organisms along the LOAC of the boreal region uncertain. There is, for example, a possibility that limitations for the growth of aquatic organisms might shift along downstream flow path, in particular when the water retention in the landscape is prolonged by a water flow through lakes Such shifts are likely if element ratios rapidly change along the LOAC, and threshold elemental ratios are reached (Frost et al 2006). For example, widely accepted that large amounts of carbon can be lost from the water column by lake sedimentation and by emission in form of carbon dioxide (CO2) and methane (CH4) (Dean and Gorham 1998; Battin et al 2009; Tranvik et al 2009; Aufdenkampe et al 2011; Raymond et al 2013)
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