Role of within-lake processes and hydrobiogeochemical changes over 16 years in a watershed in the Adirondack Mountains of New York State, USA

Hydrological and biogeochemical relationships were evaluated for the Arbutu s Watershed in the Adirondack Mountains of New York State. Wet-only precipi tation inputs (weekly) and discharge losses were evaluated from 1983 to 199 8. Precipitation from 1983-98 had significant (p < 0.05) decreases in conce ntrations of Ca2+ (-0.10 mu mol(c) l(-1) year(-1)), Mg2+ (-0.07 mu mol(c) l (-1) year(-1)), K+ (-0.01 mu mol(c) l(-1) year(-1)), Na+ (-0.04 mu mol(c) l (-1) year(-1)), Cl- (-0.07 mu mol(c) l(-1) year(-1)), SO42- (-0.82 mu mol(c ) l(-1) year(-1)) and H+ (-0.55 mu mol(c) l(-1) year(-1)), whereas NH4+ and NO3- concentrations did not change. For the same period, there were decrea ses in solute concentrations in the Arbutus Lake outlet for Ca2+ (-1.18 mu mol(c) l(-1) year(-1)), Mg2+ (-0.32 mu mol(c) l(-1) year(-1)), K+ (-0.33 mu mol(c) l(-1) year(-1)), Cl- (-0.17 mu mol(c) l(-1) year(-1)) and SO42- (-1 .90 mu mol(c) l(-1) year(-1)) and a significant increase in NH4+ concentrat ions (+0.07 mu mol(c) l(-1) year(-1)). For the period from 1995 through 199 8 the discharge measurements for the outlet and the major inlet of Arbutus Lake were combined with weekly chemical measurements supplemented with stor m sampling. At the inlet there were significant relationships (p < 0.05) be tween discharge rates and the concentrations of all solutes except Cl-, but only for Na+, NO3-, H+ and Al did these relationships explain more than 20 % of the variation in solute concentrations. April had the greatest rates o f discharge and solute Bur of any month due to spring snowmelt. The dormant season (October-May) accounted for > 80% of the discharge in the inlet and outlet of Arbutus Lake and > 78% of the flux of all solutes. For 1995-98 t he mass balances of discharge losses from the catchment draining into Arbut us Lake inlet I versus precipitation inputs suggest that internal watershed processes resulted in net generation of Ca2+ (-1342 mol(c) ha(-1) year(-1) ), Mg2+ (-313 mol(c) ha(-1) year(-1)), K+ (-35 mol(c) ha(-1) year(-1)), SO4 2- (-635 mol(c) ha(-1) year(-1)) and Cl- (-45 mol(c) ha(-1) year(-1)) and n et retention of inorganic N solutes (NO3- + NH4+: 204 mol(c) ha(-1) year(-1 )) and H+ (424 mol(c) ha(-1) year(-1)). Concentrations and fluxes of Ca2+, H+, NO3-, SO42- and Al were lower at the lake outlet compared with the inle t. A comparison of mass balances at the Arbutus Lake inlet and outlet sugge sted that these decreases may have been due to within-lake biotic processes and/or dilution from other water sources to the lake. Copyright (C) 2001 J ohn Wiley & Sons, Ltd.