The GEOMON network of Czech catchments provides long‐term insights into altered forest biogeochemistry: From acid atmospheric deposition to climate change

• Published in: Hydrological processes Vol. 35; no. 5
• Main Authors: Oulehle, Filip, Fischer, Milan, Hruška, Jakub, Chuman, Tomáš, Krám, Pavel, Navrátil, Tomáš, Tesař, Miroslav, Trnka, Miroslav
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 01.05.2021; Wiley Subscription Services, Inc
• Subjects: Acidification; Aluminium; Aluminum; Ammonia; Anions; anthropogenic activities; Anthropogenic factors; atmospheric deposition; Atmospheric pollution deposition; Bark; bark beetle infestations; Biogeochemistry; biomass; Catchments; Cations; Climate change; Czech Republic; Decline; Deposition; Dissolved organic carbon; Drought; Drought effects; Ecosystem management; Ecosystems; Eutrophication; Evaporation; Fluxes; forest damage; forest decline; forest ecosystem; Forest ecosystems; Forest management; Forests; Human influences; Hydrologic cycle; Hydrological cycle; Leaching; Nitrates; Nitrogen; Nitrogen compounds; Nitrogen oxides; Organic carbon; pH effects; Phosphorus; Precipitation; Recovery; Runoff; Soil; Soils; Strategic management; stream; Stream discharge; Stream flow; streams; Sulfur; Sulfur dioxide; sulphur; temporal variation; Temporal variations; Throughfall; total dissolved nitrogen; total phosphorus; Transpiration; Vegetation; Water balance; Water balance components; Watersheds; Czech Republic
• ISSN: 0885-6087; 1099-1085
• DOI: 10.1002/hyp.14204

In 1994, a network of small catchments (GEOMON) was established in the Czech Republic to determine input–output element fluxes in semi‐natural forest ecosystems recovering from anthropogenic acidification. The network consists from 16 catchments and the primary observations of elements fluxes were complemented by monitoring of biomass stock, element pools in soil and vegetation, and the main water balance components. Over last three decades, reductions of SO2, NOx and NH3 emissions were followed by sulphur (S) and nitrogen (N) deposition reductions of 75% and 30%, respectively. Steeper declines of strong acid anion concentrations compared to cations (Ca, Mg, Na, K, NH4) in precipitation resulted in precipitation pH increase from 4.5 to 5.2 in bulk precipitation and from 4.0 to 5.1 in spruce throughfall. Stream chemistry responded to changes in deposition: S leaching declined. However at majority of catchments soils acted as a net source of S to runoff, delaying recovery. Stream pH increased at acidic streams (pH < 6) and aluminium concentration decreased. Stream nitrate (NO3) concentration declined by 60%, considerably more than N deposition. Stream NO3 concentration was tightly positively related to stream total dissolved nitrogen to total phosphorus (P) ratio, suggesting the role of P availability on N retention. Trends in dissolved organic carbon fluxes responded to both acidification recovery and to runoff temporal variation. An exceptional drought occurred between 2014 and 2019. Over this recent period, streamflow decreased by ≈ 40% on average compared to 1990s, due to the increases of soil evaporation and vegetation transpiration by ≈ 30% and declines in precipitation by ≈ 15% on average across the elevational gradient. Sharp decreases of stream runoff at catchments <650 m a.s.l. corresponded to areas of recent forest decline caused by bark beetle infestation on drought stressed spruce forests. Understanding of the interactions among legacies of acidification and eutrophication, drought effects on the water cycle and forest disturbance dynamics is requisite for effective management of forested ecosystems under anthropogenic influence. Rapid recovery of precipitation chemistry was followed by steady recovery of acid‐base status at acidic streams (pH < 6) since 1994. Nitrate losses decreased proportionally more than measured declines in N deposition. Drought episodes altered solute fluxes and dissolved organic carbon export. Increased evapotranspiration losses caused dramatic declines in stream runoff at catchments under 650 m a.s.l. Based on documented drought and bark beetle induced forest declines, further alteration of forest biogeochemistry can be expected.