Nitrogen uptake and coupled nitrification–denitrification in riverine sediments with benthic microalgae and rooted macrophytes
- 604 Downloads
Riverine ecosystems receive nitrogen loads from point and diffuse sources that are transferred downstream. Such loads may undergo poorly explored retention and dissipation processes, varying along gradients of nitrogen availability due to different interactions among primary producers and microbial communities. We measured carbon uptake and nitrogen fluxes in microcosms containing riverine sediments with benthic algae and submerged macrophytes (Vallisneria spiralis L.). Coupled nitrification–denitrification rates were determined via 15N–NH4 + injection in the pore water and quantification of the produced 29N2 and 30N2. Two sites with different N–NO3 − concentration and sediment organic content were investigated. We hypothesized that: (1) N–NO3 − availability promotes water column N uptake and attenuates primary producers-bacteria competition; (2) coupled nitrification–denitrification is stimulated by radial oxygen loss from roots; (3) macrophyte meadows favour both temporary nitrogen retention and permanent removal. Sediments with V. spiralis were mostly inorganic C and N sinks and always displayed higher coupled nitrification–denitrification rates compared to sediments with microphytobenthos. Highest rates, up to 100 µmol N m−2 h−1, were measured at the more eutrophic site and in the light. This is likely due to a shift from root to leaf uptake at the N–NO3 − rich site, attenuating plant-bacteria competition, and to increased radial oxygen loss in organic-rich sediments, stimulating nitrification. High rates of N uptake and loss in lotic sediments represent natural buffers preventing N transport downstream and stress the need to preserve aquatic vegetation and its ecosystem services.
KeywordsSediment Vallisneria spiralis L. Rhizosphere Microphytobenthos Coupled nitrification–denitrification N-uptake
E. Racchetti was supported by FLA (Fondazione Lombardia per l’Ambiente, Lombardy Foundation for the Environment).
- Agami M, Waisel Y (1986) The ecophysiology of roots of submerged vascular plants. Physiol Veg 24:607–624Google Scholar
- Carpenter SR (1983) Submersed macrophyte community structure and internal loading: relationship to lake ecosystem productivity and succession. Lake Reserv Manag 2:105–111Google Scholar
- Dalsgaard T, Nielsen LP, Brotas V, Viaroli P, Underwood GJC, Nedwell DB, Sundbäck K, Rysgaard S, Miles A, Bartoli M, Dong L, Thornton DCO, Ottosen LDM, Castaldelli G, Risgaard-Petersen N (2000) Protocol handbook for NICE-nitrogen cycling in estuaries: a project under the EU research programme. Marine Science and Technology (MAST III), National Environmental Research Institute, SilkeborgGoogle Scholar
- Decleyre H, Heylen K, Sabbe K, Tytgat B, Deforce D, Van Nieuwerburgh F, Van Colen C, Willems A (2015) A doubling of microphytobenthos biomass coincides with a tenfold increase in denitrifier and total bacterial abundances in intertidal sediments of a temperate estuary. PLoS One 10(5):e0126583CrossRefPubMedPubMedCentralGoogle Scholar
- Flindt MR (1994) Measurements of nutrient fluxes and mass balances by on-line in situ dialysis in a Zostera marina bed culture. Verh Int Verein Theor Angew Limnol 25:2259–2264Google Scholar
- Golterman HL, Clymo RS, Ohnstand MAM (1978) Methods for physical and chemical analysis of fresh waters. Blackwell, Oxford (I.B.P. Handbook number 8) Google Scholar
- Nizzoli D, Welsh DT, Longhi D, Viaroli P (2014) Influence of Potamogeton pectinatus and microphytobenthos on benthic metabolism, nutrient fluxes and denitrification in a freshwater littoral sediment in an agricultural landscape: N assimilation versus N removal. Hydrobiologia 737(1):183–200CrossRefGoogle Scholar
- Pierobon E, Castaldelli G, Matovani S, Vincenzi F, Fano EA (2013) Nitrogen removal in vegetated and unvegetated drainage ditches impacted by diffuse and point sources of pollution. Clean 41(1):24–31Google Scholar
- Risgaard-Petersen N (2003) Coupled nitrification–denitrification in autotrophic and heterotrophic estuarine sediments: on the influence of benthic microalgae. Limnol Oceanogr 48(1I):93–105Google Scholar
- Wang C, Yan X, Wang P, Chen C (2008) Interactive Influence of N and P on their uptake by four different hydrophyte. Afr J Biotechnol 7(19):3480–3486Google Scholar