Back from the past? Assessment of nitrogen removal ability of buried historic wetland soils before and after a 1-year incubation on a restored floodplain

Stream, floodplain, and wetland restorations enhance water quality and ecological function; however, soil health is prioritized infrequently in restoration planning and monitoring. Buried, historic, hydric soils—common across U.S. mid-Atlantic valley bottoms beneath legacy sediments—are not included in most floodplain restoration designs, though they may retain favorable biogeochemical characteristics and host legacy microbial communities that could support ecosystem recovery if exhumed and preserved. To assess the efficacy of including historic hydric soils in floodplain restoration for nitrogen (N) removal, we characterized pre-Euro-American settlement wetland soils buried below legacy sediments and now exposed along incised streambanks across the mid-Atlantic. We compared carbon (C) and N contents; C:N ratios; nitrate-N and ammonium-N concentrations; denitrification rates; functional genes for denitrification (nosZ) and nitrification (amoA for ammonia oxidizing archaea [AoA] + ammonia oxidizing bacteria [AoB]); and phospholipid fatty acid biomasses of historic wetland soils with contemporary wetland soils before and after an 1-year incubation in a recently restored floodplain. Compared to modern wetland soils, historic hydric soils buried by legacy sediment are less nutrient-rich, have fewer functional genes for and lower rates of denitrification, and possess significantly less microbial biomass. Following the 1-year incubation, many of these concentrations, rates, and gene counts increased in historic soils, though not substantially. Ultimately, our results suggest that while inclusion of historic, hydric soils and their legacy microbiomes is valuable for N-removal in floodplain restoration, the recovery of historic, hydric soils is predictably slow, and attainment of restoration goals, such as increased denitrification, may require multiple years.     

Spatial heterogeneity in water velocity drives leaf litter dynamics in streams

1. Stream hydro-morphology refers to the heterogeneous distribution of hydrologic conditions that occur above a complex benthic surface such as a streambed.
2. We hypothesised that hydro-morphological conditions will influence the retention, re-distribution, and microbial-driven decomposition of leaf litter inputs in stream ecosystems because each process varies with overlying water velocity.
3. We tested this hypothesis using: (1) the spatial distribution of water velocity within a stream reach as a surrogate of stream hydro-morphology; (2) leaf tracer (i.e. Ginkgo biloba L.) additions with serial recovery to examine the relationship between benthic retention and overlying velocity; and (3) measurements of leaf litter decomposition (i.e. Alnus glutinosa [L.] Gaertn.) under different water velocity conditions.
4. Results demonstrate that water velocity exerts a significant influence on the retention and re-distribution of leaf litter inputs within the reach. The observed range of water velocity (from c. 0 to 0.92 cm/s) also strongly influences the range of leaf litter decomposition rates (0.0076–0.0222/day).
5. Our findings illustrate that water velocity influences leaf litter dynamics in streams by controlling leaf litter transport, retention and re-distribution as well as how leaves decompose within recipient stream reaches. Ultimately, the results show that the efficiency of leaf litter inputs in supporting stream ecosystem function is dependent on the hydro-morphological characteristics of the receiving stream ecosystems.

     

Biophysical Heterogeneity,Hydrologic Connectivity,and Productivity of a Montane Floodplain Forest

Ecosystems - Floodplains display exceptional variation in habitat type, connectivity, and vegetation structure that make them ideal landscapes in which to address biophysical controls on primary...