Forest Soils and Biogeochemistry ¶

• Le acque sotterranee provenienti dalle aree forestali sono solitamente di qualità tale da poter essere immesse nella rete dell'acqua potabile senza ulteriori trattamenti.
• Il dilavamento dei nitrati dal suolo forestale nell'ultimo decennio non ha subito variazioni. Tuttavia, localmente può essere elevato e indicare un eccessivo carico di azoto.
• Per abbattere le concentrazioni di nitrato nell'acqua di falda e quindi in quella potabile, occorre ridurre gli apporti di azoto atmosferico. Le misure selvicolturali che rafforzano la resilienza dei boschi possono anche ridurre il rischio di dilavamento dei nitrati in seguito a perturbazioni.

• The groundwater from forest areas is usually of such good quality that it can be fed into the drinking water network without further treatment.
• Levels of nitrate leaching from forest soils have hardly changed in the past decade. However, they can be high in some localities, indicating an excessive nitrogen load.
• In order to lower nitrate concentrations in seepage water and thus in drinking water from forest areas, nitrogen deposition from the air must be reduced. Silvicultural measures that strengthen forests’ resilience can also reduce the risk of nitrate leaching after disturbance events.

• Les eaux souterraines des zones forestières sont en général de si bonne qualité qu'elles peuvent être injectées sans traitement dans le réseau d'eau potable.
• Le lessivage des nitrates des sols forestiers n'a guère évolué durant la dernière décennie. Il peut être localement élevé, signalant une charge excessive d'azote.
• Pour abaisser la concentration de nitrates dans les eaux d'infiltration et donc dans l'eau potable de zones forestières, les dépôts atmosphériques azotés doivent être réduits. Des mesures sylvicoles renforçant la résilience de la forêt permettent de limiter le risque de lessivage de nitrates après des perturbations.

• Das Grundwasser aus Waldgebieten ist meist von so guter Qualität, dass es ohne weitere Aufbereitung ins Trinkwassernetz eingespeist werden kann.
• Die Nitratauswaschung aus den Waldböden hat sich in der letzten Dekade kaum verändert. Sie kann jedoch lokal hoch sein und weist auf eine übermässige Stickstoffbelastung hin.
• Um die Nitratkonzentrationen im Sickerwasser und damit im Trinkwasser aus Waldgebieten zu senken, ist die Reduktion der Stickstoffeinträge aus der Luft erforderlich. Mit waldbaulichen Massnahmen, die die Resilienz der Wälder stärken, lässt sich zudem das Risiko der Nitratauswaschung nach Störungsereignissen verringern.

• Reliable insights from key δ²H bioindicators, n-alkanes and carbohydrates, are hindered by our limited understanding of isotope fractionation processes related to leaf water and primary assimilates. We addressed this with the first study to investigate time-integrated intra-annual δ²H signals of n-alkanes and carbohydrates in a natural forest.
• We sampled 1-yr-old needles (1N) and current-year needles (0N) from five Scots Pine trees in a coniferous forest in Hyytiälä, Finland, biweekly during 2019. The δ²H of their n-alkanes (δ²H_alkane), water-soluble carbohydrates (δ²H_WSC) and starch (δ²H_starch) were evaluated for time-integrated physiological (gas-exchange) and environmental (hydrological) signals.
Time integration was critical for interpreting δ²H_WSC and δ²H_alkane.
• Time-integrated net assimilation rate (T:A_n), the strongest signal in δ²H_WSC, correlated negatively with 1N δ²H_WSC (early season) and positively with 0N δ²H_WSC (late season). Unexpectedly, δ²H_alkane exhibited stronger environmental signals in 1N than in 0N, with the most pronounced being physiologically mediated hydrological signals.
• T:A_n is a major signal in intra-annual δ²H_WSC in a boreal forest, subject to seasonal interactions with needle age and δ²H_starch. There could be enough de novo n-alkane synthesis in situ to enhance the reliability of δ²H_alkane as a hydrological indicator, bringing promise to interpretations of the n-alkane palaeohydrological record.