The biogeochemistry of potassium at Hubbard Brook

Abstract

Abstract. A synthesis of the biogeochemistry of K was conducted during in the reference and human-manipulated watershed-ecosystems of the Hubbard Brook Experimental Forest (HBEF), NH. Results showed that during the first two years of the study , which coincided with a drought period, the reference watershed was a net sink for atmospheric inputs of K. During the remaining years, this watershed has been a net source of K for downstream ecosystems. There have been long-term declines in volume-weighted concentration and flux of K at the HBEF; however, this pattern appears to be controlled by the relatively large inputs during the initial drought years. Net ecosystem loss (atmospheric deposition minus stream outflow) showed an increasing trend of net loss, peaking during the mid-1970s and declining thereafter. This pattern of net K loss coincides with trends in the drainage efflux of SO: and NO;, indicating that concentrations of strong acid anions may be important controls of dissolved K loss from the site. There were no long-term trends in streamwater concentration or flux of K. A distinct pattern in pools and fluxes of K was evident based on biotic controls in the upper ecosystem strata (canopy, boles, forest floor) and abiotic controls in lower strata of the ecosystem (mineral soil, glacial till). This biological control was manifested through higher concentrations and fluxes of K in vegetation, aboveground litter, throughfall and forest floor pools and soil water in the northern hardwood vegetation within the lower reaches of the watershedecosystem, when compared with patterns in the high-elevation spruce-fir zone. Abiotic control mechanisms were evident through longitudinal variations in soil cation exchange capacity (related to soil organic matter) and soil/till depth, and temporal and disturbance-related variations in inputs of strong-acid anions. Marked differences in the K cycle were evident at the HBEF for the periods 1964-69 and 1987-92. These changes included decreases in biomass storage, net mineralization and throughfall fluxes and increased resorption in the latter period. These patterns seem to reflect an ecosystem response to decreasing rates of biomass accretion during the study. Clearcutting disturbance resulted in large losses of K in stream water and from the removal of harvest products. Stream losses occur from release from slash, decomposition of soil organic matter and displacement from cation exchange sites. Elevated concentrations of K persist in stream water for many years after clearcutting. Of the major elements, K shows the slowest recovery from clearcutting disturbance.

Sulfate exports from multiple catchments in a glaciated forested watershed in western New York, USA

“…Atmospheric deposition of sulfate (SO 2À 4 ) in the northeastern United States (US) has shown a decreasing trend over the last few decades (Likens et al 2002). Although stream concentrations in most watersheds are also declining (Likens et al 2002), the mass exports of SO 2À 4 from others continue to exceed the inputs of SO 2À 4 from atmospheric deposition (Hornbeck et al 1997;Likens et al 2002).…”

“…Although stream concentrations in most watersheds are also declining (Likens et al 2002), the mass exports of SO 2À 4 from others continue to exceed the inputs of SO 2À 4 from atmospheric deposition (Hornbeck et al 1997;Likens et al 2002). The reasons for these mass balance discrepancies has not been completely ascertained, but possibilities include: (1) unaccounted inputs of dry deposition (Edwards et al 1999;Likens et al 2002); (2) net mineralization of sulfur (S) from soil organic matter (Eimers and Dillon 2002;Eimers et al 2004;Shanley et al 2005); (3) desorption of SO 2Àsoils that previously adsorbed SO 2À 4 during elevated periods of deposition (Alewell et al 1999;Eimers and Dillon 2002;Eimers et al 2004); (4) weathering of primary S minerals from geological substrate (Bailey et al 2004;Baron et al 1995;Mitchell et al 2001a); and (5) release of SO 2À 4 due to oxidation of reduced sulfide from wetlands (Bayley et al 1986;Hill 1997, 1999;Lazerte 1993;Mitchell et al 2006;Warren et al 2001).…”

Natural and anthropogenic drivers of calcium depletion in a northern forest during the last millennium

“…Calcium concentrations were declining before Euro-American settlement, and it is difficult to assess the role of anthropogenic activities in the 20th century from these sedimentary data alone. Nevertheless, this decrease in sedimentary Ca from 876 CE to the beginning of the presettlement period reflects a large depletion of the total Ca pool from upper soil horizons, and this pool remains a particular concern, as it is larger than the entire exchangeable Ca pool in the soil and the forest floor pool (10,25). …”

“…As a base cation, soil Ca 2+ is highly sensitive to pH, and several mechanisms that acidify soil could lead to the development of Ca limitation (10). Understanding nutrient limitation requires consideration of multiple elements, including macronutrients and rock-derived elements such as Al, Si, Ca, Na, Mg, and K. Acid rain-atmospheric deposition of all wet and dry substances that cause acidification-commenced in Europe and eastern North America in the middle of the 20th century and caused nutrient leaching from soils (11).…”

Steep spatial gradients of volcanic and marine sulfur in Hawaiian rainfall and ecosystems

“…In coastal settings and locations downwind from anthropogenic activities like fossil fuel burning, sulfur limitation is less likely; inland areas and zones where greater rainfall promotes greater leaching are more likely to experience sulfur deficiency (Tisdale et al, 1986). In undisturbed ecosystems, atmospheric deposition in excess of demand should result in rapid 'flow-through' losses of sulfur (Likens et al, 2002), whereas if demand exceeds atmospheric deposition, more efficient recycling should result.…”