Magnitudes and controls of organic and inorganic carbon flux through a chain of hard‐water lakes on the northern Great Plains

Abstract

Whole-lake carbon (C) mass-balance budgets were constructed for a chain of six hard-water lakes to quantify the relative importance of organic carbon (OC) and inorganic carbon (IC) exchanges between atmosphere, water column, sediments, and rivers. Mean summer C fluxes were calculated for each lake during the ice-free periods (May to September) of 1995-2007 by measuring deposition of IC and OC in lake sediments, export of C to outflow rivers, lotic C influxes, and atmospheric exchange of CO 2 . Unlike soft-water lakes, IC in rivers accounted for 68.2-85.6% of total C (TC) influx to these hard-water lakes, CO 2 efflux accounted for 0-44.5% of total C export (median 2.8%), and sedimentation buried similar amounts of OC and IC. Deposition of C in sediments accounted for 1.8-61.7% of total export and was correlated to water residence time, while C efflux through rivers accounted for 32.6-98.2% of total export, mainly as IC (69.6-85.1% of TC). Unexpectedly, estimates of net ecosystem production based on OC mass balances suggested that all lakes were autotrophic (production . respiration) during summer, despite elevated dissolved organic carbon content (5.6-16.1 mg C L 21 ), pCO 2 values, and net CO 2 emissions to the atmosphere from three lakes. We conclude that C fluxes within and among these hard-water lakes are regulated by hydrologic inputs of dissolved IC rather than by lake metabolism, IC and OC pathways are only loosely coupled, and future climate variability will alter C fluxes in similar lakes mainly through regulation of mass transfer from land.

Contribution of sediment focussing to heterogeneity of organic carbon and phosphorus burial in small lakes

“…As many carbon burial rate studies are explicitly sampled at the deepest point in the lake or areas where sediment accumulation is most rapid (e.g. Downing et al, 2008;Anderson et al, 2009;Finlay et al, 2010), these values should therefore be regarded as maximum burial rates and not necessarily representative of the whole lake. This qualification of organic carbon burial is important for comparing between lakes and especially when assessing the overall importance of lakes in global carbon burial (e.g.…”

“…While spatial heterogeneity in sediment is widely recognised, the estimation of burial rates or lake-wide fluxes of materials such as organic carbon do not often reflect this (e.g. Downing et al, 2008;Anderson, D'Andrea & Fritz, 2009;Finlay et al, 2010). Similarly, the general applicability of existing models used to explain this spatial heterogeneity still needs to be demonstrated, particularly in the case of small lakes.…”

The effects of river inflow and retention time on the spatial heterogeneity of chlorophyll and water–air CO<sub>2</sub> fluxes in a tropical hydropower reservoir

“…Additionally, hydrodynamics factors, such as retention time and river inflow, may influence the phytoplankton communities and their growth (Vidal et al, 2012;Soares et al, 2008). Intense phytoplankton primary production has been identified as the main regulator of carbon (C) budgets in temperate eutrophic lakes (Finlay et al, 2010;Pacheco et al, 2014); however, the impact of these communities on tropical hydropower reservoirs is still unclear.…”

Atmospheric Deposition of Nutrients Shifts Carbon Capture and Storage Trends in Freshwater Tropical Lakes in India

“…Significant increases in change ratio (P 0.01 to P 0.001) from study year 6 (2004) afterward indicate C accumulation over time. The DOC may be mineralized to dissolve inorganic carbon (DIC) and released to the atmosphere or settles as particulate organic carbon (POC) and stored in sediments (Porcal et al, 2009;Finlay et al, 2010). Carbon accumulation appeared more pronounced for lake Baghdara where, during the final study year, sediment TOC increased by over 2 folds.…”