Importance of within-lake processes in affecting the dynamics of dissolved organic carbon and dissolved organic and inorganic nitrogen in an Adirondack forested lake/watershed

Abstract

Abstract. Lakes nested in forested watersheds play an important role in mediating the concentrations and fluxes of dissolved organic matter. We compared long-term patterns of concentrations and fluxes of dissolved organic carbon (DOC) and dissolved organic (DON) and inorganic nitrogen (DIN) in aquatic ecosystems of the Arbutus Lake watershed to evaluate how a lake nested in a forested watershed affects the sources (e.g., production) and sinks (e.g., retention) of DOC and DON in the Adirondack Mountains of New York, USA. We observed no significant long-term changes of DOC and DON in the lake outlet since 1983 and 1994, respectively. However, the temporal patterns of DOC and DON concentrations in the lake inlet showed significant seasonality such as increases during the vegetationgrowing season along with notable decreases in the dormant season. A comparison of mass balances between inlet and outlet for the period from 2000 to 2009 suggested that the lake was a sink of DOC (mean of influx minus outflux: +1140 mol C ha −1 yr −1 ). In contrast, the difference of discharge-weighted DON concentrations (mean of inlet minus outlet: −1.0 µmol N L −1 ) between inlet and outlet was much smaller than the discharge-weighted DOC concentrations (average of inlet minus outlet: + 87 µmol C L −1 ). DON fluxes showed considerable variation among years (mean of influx minus outflux: +8 mol N ha −1 yr −1 ; range of differences: −15 to 27 mol N ha −1 yr −1 ). DON exhibited low percent retention ((influx-outflux)/influx) (mean: 6.9 %, range: −34.8 to +31.2) compared to DOC (mean: 30.1 %, range: +9.2 to +44.1). The resultant increase of DON within the lake was closely linked with a net decrease of DIN through monthly Pearson correlation analysis, suggesting the importance of biotic factors in mediating lake DON dynamics. Our results show different relative retentions of DOC compared with DON, along with a larger retention of DIN than DON, suggesting that DOC and DON might display substantially different biogeochemical relationships in oligo-mesotrophic lakes nested forested watersheds and therefore different roles for a sink behavior for DOC compared to a producer of DON.

Climate‐induced hydrological variation controls the transformation of dissolved organic matter in a subalpine lake

“…A similar buffering behavior has been described in oligotrophic mountain lakes, both for dissolved (Goodman et al 2011;Kang et al 2016) and particulate (Epstein et al 2013) organic matter, as well as inorganic nutrients (Wurtsbaugh et al 2005;Brown et al 2008). However, our nearly balanced DOC mass balance contrasts with the common finding of clear-water lakes as a source of DOC (Kling et al 2000;Brown et al 2008;Epstein et al 2013;Kalinin et al 2016).…”

Landscape Influence on the Browning of a Lake Watershed in the Adirondack Region of New York, USA

“…This pattern suggests that terrestrial DOM sources are driving DOC increases during the growing season as temperatures increase and discharge from the surrounding watershed decreases (Table 1) [31]. Previous observations of decreasing DOC fluxes in the lake between the months of March-November [32] align with patterns of decreasing terrestrial DOM fractions (Figure 5b,c. Concurrently, reprocessed DOM fractions increased substantially during the summer period (Figure 5d).…”

“…Discharge at the Archer Creek inlet to Arbutus Lake has been measured since 1994 using an H-flume. Major solutes were measured in the Biogeochemistry Laboratory (SUNY-ESF), which participates with the US Geological Survey quality assurance/quality control (QA/QC) program, in accordance with long-term measurements at Huntington Forest [32]. Samples were filtered with a Durapore ® 0.45 µm polyvinylidene difluoride (PVDF) membrane.…”

“…The Arbutus Lake watershed within the Adirondack Mountains of New York State has been a site for long-term biogeochemical studies, including DOC mass budgets [30] and initial investigations into carbon quality at both the watershed [31] and in-lake spatial patterns [32]. Arbutus, like many Adirondack lakes, is experiencing long term increases in DOC [12].…”

Dissolved organic N in shallow tropical lakes and reservoirs: Contribution to total dissolved N and relationships with eutrophication

“…Concentration of DON in the Casa de Pedra reservoir and Lake CTan were higher in the rainy season than in the dry season, suggesting either leaching of allochthonous catchment organic material to these lakes, or excretion or lysis by phytoplankton or zooplankton in this period of increased primary productivity (Zehr, Paulsen, Axler, & Goldman, ). Internal processes, such as excretion, lysis, or decomposition, are, however, often described as being more important for lake DOM dynamics during the dry season (Kang et al, ).…”