A network of 15 Surface Elevation Tables (SETs) at North Inlet estuary, South Carolina, has been monitored on annual or monthly time scales beginning from 1990 to 1996 and continuing through 2022. Of 73 time series in control plots, 12 had elevation gains equal to or exceeding the local rate of sea-level rise (SLR, 0.34 cm/year). Rising marsh elevation in North Inlet is dominated by organic production and, we hypothesize, is proportional to net ecosystem production. The rate of elevation gain was 0.47 cm/year in plots experimentally fertilized for 10 years with N&P compared to nearby control plots that have gained 0.1 cm/year in 26 years. The excess gains and losses of elevation in fertilized plots were accounted for by changes in belowground biomass and turnover. This is supported by bioassay experiments in marsh organs where at age 2 the belowground biomass of fertilized
The dynamics of soil phosphorus (P) control its bioavailability. Yet it remains a challenge to quantify soil P dynamics. Here we developed a soil P dynamics (SPD) model. We then assimilated eight data sets of 426‐day changes in Hedley P fractions into the SPD model, to quantify the dynamics of six major P pools in eight soil samples that are representative of a wide type of soils. The performance of our SPD model was better for labile P, secondary mineral P, and occluded P than for nonoccluded organic P (Po) and primary mineral P. All parameters describing soil P dynamics were approximately constrained by the data sets. The average turnover rates were labile P 0.040 g g−1day−1, nonoccluded Po 0.051 g g−1day−1, secondary mineral P 0.023 g g−1day−1, primary mineral P 0.00088 g g−1day−1, occluded Po 0.0066 g g−1day−1, and occluded inorganic P 0.0065 g g−1day−1, in the greenhouse environment studied. Labile P was transferred on average more to nonoccluded Po (transfer coefficient of 0.42) and secondary mineral P (0.38) than to plants (0.20). Soil pH and organic C concentration were the key soil properties regulating the competition for P between plants and soil secondary minerals. The turnover rate of labile P was positively correlated with that of nonoccluded Po and secondary mineral P. The pool size of labile P was most sensitive to its turnover rate. Overall, we suggest data assimilation can contribute significantly to an improved understanding of soil P dynamics.
more » « less- Award ID(s):
- 1655499
- NSF-PAR ID:
- 10447893
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Biogeosciences
- Volume:
- 124
- Issue:
- 7
- ISSN:
- 2169-8953
- Page Range / eLocation ID:
- p. 2159-2173
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract S. alterniflora plants was increasing by 1,994 g m−2 year−1, which added a growth premium of 2.4 cm/year to elevation gain. This was contrasted with the net belowground growth of 746 g m−2 year−1in controls, which can add 0.89 cm/year to elevation. Root biomass density was greater in the fertilized bioassay treatments than in controls, plateauing at about 1,374 g m−2and 472 g m−2, respectively. Growth of belowground biomass was dominated by rhizomes, which grew to 3,648 g m−2in the fertilized treatments after 3 years and 1,439 g m−2in the control treatments after 5 years. Depositional wetlands are limited by an exogenous supply of mineral sediment, whereas marshes like North Inlet could be classified as autonomous because they depend on in situ organic production to maintain elevation. Autonomous wetlands are more vulnerable to SLR because their elevation gains are constrained ultimately by photosynthetic efficiency. -
more » « less
Abstract Fluvial erosion of cohesive soil is mediated by interactions between soil physical, biological, and chemical characteristics such as soil aggregate stability and extracellular polymeric substances (EPS). While labile organic matter (OM) stimulates microbial EPS production and significantly improves soil aggregate stability in agricultural soils, these interactions remain unexplored in streambank soils. The study goal was to quantify the impact of OM on aggregate stability, EPS, and fluvial erosion rates of cohesive streambank soil. Increasing amounts of 1‐mm sieved dry grass were incorporated at rates of 0, 1, and 4 g per 100 g of 2‐mm sieved silt‐loam soil (treatments T0, T1, and T4, respectively). Samples (eight replicates per treatment) were matured in a greenhouse for 50 days prior to flume erosion testing. EPS carbohydrates were significantly (
p < 0.05) lower in T1 (324 ± 63 μg/g) compared to T0 (388 ± 37 μg/g) and T4 (376 ± 44 μg/g). EPS proteins were significantly higher in T1 (194 ± 15 μg/g) and T4 (223 ± 61 μg/g) compared to T0 (101 ± 20 μg/g) and positively correlated with mean weight diameter (MWD), a measure of soil stability against slaking. MWD was 16% and over 100% higher for T1 and T4, respectively, than for T0. Similarly, the average soil erodibility coefficient of T1 and T4 was 25% and 61% lower than the erodibility of T0; however, only the reduction for T4 was significant. The data presented here underscore the important role labile OM plays in improving soil physical stability and increasing the resistance of cohesive soil to fluvial erosion of streambanks. -
more » « less
Abstract Environmental factors such as nutrient and light availability may play important roles in determining the magnitude and direction of microbial priming and detrital decomposition and, therefore, the relative importance of microbial priming in carbon (C) dynamics in freshwater ecosystems.
We integrated light availability with an existing conceptual model predicting the magnitude of the priming effect (PE) along a dissolved nutrient gradient (i.e.
nutrient PE model). Our modifiedlight‐nutrient PE model hypothesises how light may mediate priming at any given nutrient concentration and provides a calculation method for quantitative PE values (i.e. light effect size at a given nutrient concentration).We used recirculating stream mesocosms with
Quercus stellata (post oak) leaf litter as an organic matter (OM) substrate in a 150‐day experiment to test our model predictions. We manipulated light levels [ambient (full light), shaded (c. 19% of ambient)] and phosphorus (P) concentration (10, 100, 500 µg PO4‐P/L) in a fully factorial design. We also supplied all mesocosms with 500 µg/L dissolved inorganic nitrogen. Microbial biomass, water column dissolved organic C, and leaf litter dry mass and recalcitrant OM [i.e. the fibre (cellulose + lignin) component of post oak substrate] were measured. Recalcitrant OM (ROM)k ‐rates (day−1) were used to calculate the light effect size within P treatments as a log response ratio (ln [ambientk ‐rate/shadek ‐rate]) to ascertain PE magnitude and direction (positive or negative).Light was an important driver of dissolved organic C, a potential source of additional labile organic matter essential for priming heterotrophic microbes. There were weak PEs in total leaf litter dry mass remaining, but PEs were more pronounced in leaf litter ROM remaining. The strongest positive PEs (specific to litter ROM pools) occur in the highest P treatment, presumably due to a change in which nutrient, nitrogen versus P, was a limiting factor for microbes based on nutrient ratios rather than P concentration alone. These results illustrate the importance of considering light levels, nutrient ratios (rather than individual nutrients), and detrital ROM components in further PE model development.
-
more » « less
Abstract Northern peatlands are a large C stock and often act as a C sink, but are susceptible to climate warming. To understand the role of peatlands in the global carbon‐climate feedback, it is necessary to accurately quantify their C stock changes and decomposition. In this study, a process‐based model, the Peatland Terrestrial Ecosystem Model, is used to simulate pan‐Arctic peatland C dynamics from 15 ka BP to 1990. To improve the accuracy of the simulation, spatially explicit water run‐on and run‐off processes were considered, four different pan‐Arctic peatland extent data sets were used, and a spatially explicit peat basal date data set was developed using a neural network approach. The model was calibrated against 2055 peat thickness observations and the parameters were interpolated to the pan‐Arctic region. Using the model, we estimate that, in 1990, the pan‐Arctic peatlands soil C stock was 396–421 Pg C, and the Holocene average C accumulation rate was 22.9 g C·m−2 yr−1. Our estimated peat permafrost development history generally agrees with multi‐proxy‐based paleo‐climate data sets and core‐derived permafrost areal dynamics. Under Anthropocene warming, in the freeze‐thaw and permafrost‐free regions, the peat C accumulation rate decreased, but it increased in permafrost regions. Our study suggests that if current permafrost regions switch to permafrost‐free conditions in a warming future, the peat C accumulation rate of the entire pan‐Arctic region will decrease, but the sink and source activities of these peatlands are still uncertain.
-
more » « less
We assessed the relationship between rates of biological energy utilization and the biomass sustained by that energy utilization, at both the organism and biosphere level. We compiled a dataset comprising >10,000 basal, field, and maximum metabolic rate measurements made on >2,900 individual species, and, in parallel, we quantified rates of energy utilization, on a biomass-normalized basis, by the global biosphere and by its major marine and terrestrial components. The organism-level data, which are dominated by animal species, have a geometric mean among basal metabolic rates of 0.012 W (g C)−1and an overall range of more than six orders of magnitude. The biosphere as a whole uses energy at an average rate of 0.005 W (g C)−1but exhibits a five order of magnitude range among its components, from 0.00002 W (g C)−1for global marine subsurface sediments to 2.3 W (g C)−1for global marine primary producers. While the average is set primarily by plants and microorganisms, and by the impact of humanity upon those populations, the extremes reflect systems populated almost exclusively by microbes. Mass-normalized energy utilization rates correlate strongly with rates of biomass carbon turnover. Based on our estimates of energy utilization rates in the biosphere, this correlation predicts global mean biomass carbon turnover rates of ~2.3 y−1for terrestrial soil biota, ~8.5 y−1for marine water column biota, and ~1.0 y−1and ~0.01 y−1for marine sediment biota in the 0 to 0.1 m and >0.1 m depth intervals, respectively.
