Supplemental Material: Lithium isotopic composition of soil pore water: Responses to evapotranspiration

Data table and supplemental methods.

Supplemental Material: Lithium isotopic composition of soil pore water: Responses to evapotranspiration

Data table and supplemental methods.

High Temporal and Spatial Nitrate Variability on an Alaskan Hillslope Dominated by Alder Shrubs

In Arctic ecosystems, increasing temperatures are driving the expansion of nitrogen (N) fixing shrubs across tundra landscapes. The implications of this expansion to the biogeochemistry of Arctic ecosystems is of critical importance, yet many details about the form, location, and availability of N from these shrubs remain unknown. To address this knowledge gap, the spatiotemporal variability of nitrate (NO3−) and its environmental and edaphic controls were investigated at an alder (Alnus viridis spp. fruticosa) dominated permafrost tundra landscape in the Seward Peninsula, Alaska, USA. Soil pore water was collected from locations within alder shrubland growing along a well-drained hillslope and compared to soil pore water collected from locations outside (upslope, downslope, and between) the alder shrubland. δ15N and δ18O of soil pore water were consistent with the predicted range of NO3− produced through microbial degradation of N-rich alder shrub organic matter. Soil pore water collected within alder shrubland had an average NO3− concentration of (4.27 ± 8.02 mg L−1) and differed significantly from locations outside alder shrubland (0.23 ± 0.83 mg L−1; p < 0.05). Temporal variation in NO3− within and downslope of alder shrubland corresponded to precipitation events, where NO3− accumulated in the soil was flushed downslope during rainfall. Enrichment of both δ15N and δ18O isotopes at wetter downslope locations indicate that denitrification buffered the mobility and spatial extent of NO3−. These findings have important implications for nutrient production and mobility in N-limited permafrost systems that are experiencing shrub expansion in response to a warming Arctic.

A New Approach to Establish Safe Levels of Available Metals in Soil With Respect to Potential Health Hazard of Human

Safe levels of extractable pollutant elements in soil have not been universally established. Prediction of metal solubility in polluted soils and the subsequent transfer of these metals from soil pore water to the human food supply via crops are required for effective risk assessment from polluted soils. Thus an attempt has been made to develop a novel approach to protect human health from exposure to toxic metals through assessing risk from metal polluted soils utilised for agriculture. In this study, we assess the relative efficacy of various forms of ‘free ion activity model’ (FIAM) for predicting the concentration of cadmium (Cd), lead (Pb), nickel (Ni), zinc (Zn) and copper (Cu) in spinach and wheat as example crops, thereby providing an assessment of risk to human health from consumption of these crops. Free metal ion activity in soil solution was estimated using the Windermere Humic Aqueous Model VII (WHAM-VII) and the Baker soil test. Approximately 91, 81, 75, 94 and 70% of the variability in Cd, Pb, Ni, Zn and Cu content, respectively, of spinach could be described by a FIAM using an estimate of the free ion activity of the metals provided by WHAM-VII. Higher prediction coefficients were obtained using EDTA, rather than DTPA, as the metal extractant in an integrated solubility-FIAM model. Out of three formulations, the FIAM, based on free ion activity of metals in soil pore water, determined from solution extracted with Rhizon samplers, was distinctly superior to the other formulations in predicting metal uptake by spinach and wheat. A safe level of extractable metal in soil was prescribed using a hazard quotient derived from predicted plant metal content and estimated dietary intake of wheat and spinach by a human population.

The Effects of Forest Litter and Waterlogging on the Ecotoxicity of Soils Strongly Enriched in Arsenic in a Historical Mining Site

This study examined the effects of waterlogging and forest litter introduced to soil on chemical properties of soil pore water and ecotoxicity of soils highly enriched in As. These effects were examined in a 21-day incubation experiment. Tested soil samples were collected from Złoty Stok, a historical centre of arsenic and gold mining: from a forested part of the Orchid Dump (19,600 mg/kg As) and from a less contaminated site situated in a neighboring forest (2020 mg/kg As). An unpolluted soil was used as control. The concentrations of As, Fe and Mn in soil pore water were measured together with a redox potential Eh. A battery of ecotoxicological tests, including a bioassay with luminescence bacteria Vibrio fischeri (Microtox) and several tests on crustaceans (Rapidtox, Thamnotox and Ostracodtox tests), was used to assess soil ecotoxicity. The bioassays with crustaceans (T. platyurus, H. incongruens) were more sensitive than the bacterial test Microtox. The study confirmed that the input of forest litter into the soil may significantly increase the effects of toxicity. Waterlogged conditions facilitated a release of As into pore water, and the addition of forest litter accelerated this effect thus causing increased toxicity.

The effects of organic matter and flooding on the ecotoxicity of pore water in soils developed in the sites of historical arsenic mining: application of biological tests with crustacean zooplankton

&lt;p&gt;Arsenic is a trace metalloid, potentially toxic for humans, animals and for plants. The problem of soil pollution with arsenic occurs in Poland only on a local scale, but in the Sudetes and in their foreland, there are several sites were arsenic was mined in the past. Particularly high concentrations of As in soils were confirmed in Z&amp;#322;oty Stok, formerly the main European centre of arsenic industry. Decomposing forest litter as well as flooding can affect mobilization of As and other toxic elements, change their speciation in pore water and influence the toxicity to biota. This study examined the chemistry and ecotoxicity of pore water acquired from two soils that developed in a former As mining site: from the &amp;#8220;Orchid dump&amp;#8221; and from a nearby forest. Soils used in the experiment&amp;#160; contained very high concentrations of As: 2020 and 19600 mg/kg.&amp;#160; An unpolluted soil was used as a control. Soil samples were incubated in various moisture conditions (70% &amp;#160;of water holding capacity and 100% flooding), in the presence and absence of organic matter introduced with forest litter collected from a beech stand. Soil pore water was collected three times (after 7, 21 and 90 days) with MacroRhizon suction samplers. Chemical analysis of pore water involved the measurements of concentrations of As and potentially toxic metals, including Mn and Fe, as well as the concentrations of P. Ecotoxicity of pore water was examined in two bioassays: THAMNOTOXKIT F and RAPIDTOXKIT F. The Thamnocephalus platyurus toxicity test is a 24h bioassay based on the mortality of the test organisms (freshwater crustaceans). The sublethal effects were determined using RAPIDOTOXKIT, based on ISO standard 2011. This procedure measures the feeding inhibition of the juveniles of T. platyurus. A very high toxicity to T. platyurus was confirmed in the pore water of the soil richer in As, where all the organisms died. High mortality of crustaceans &gt; 83,33 % was found in the pore water of soil collected from the Orchid dump, in particular after a longer incubation period. The addition of beech litter, as well as soil flooding, caused an increased mortality of test organisms that reached 100%, regardless of the time of incubation. In the pore water of less polluted soil, collected from the forest site in Z&amp;#322;oty Stok, an increased mortality of crustaceans was observed upon the addition of beech litter. The RAPIDOTOXKIT test turned out less sensitive to high concentrations of As and other toxic components present in soil pore water. The feeding inhibition did not correspond directly with the concentrations of As. However, in the case of samples with the highest As concentration (130 mg/L), found in pore water of the Orchid dump soil treated with beech litter and fully flooded, the feeding inhibition reached 100%.&lt;/p&gt;&lt;p&gt;This research was funded by the National Science Centre of Poland; Project No. 2016/21/B/ST10/02221&lt;/p&gt;

Soil enzymes are preferentially associated with larger particles in highly organic Arctic tundra soils

Microbial processes, including extracellular enzyme (exoenzyme) production, are a major driver of decomposition and a current topic of interest in Arctic soils due to the effects of climate warming. While enzyme activity levels are often assessed, we lack information on the specific location of these exoenzymes within the soil matrix. Identifying the locations of different soil enzymes is needed to improve our understanding of microbial and overall ecosystem function. Using soil obtained from Utqiaġvik, Alaska, our objectives in the study are (1) to measure the activity of enzymes in soil pore water, (2) to examine the distribution of activity among soil particle size fractions using filtration, and (3) to cross these particle size fraction analyses with disruption techniques (blending to shred and sonication to further separate clumped/aggregated soil materials) to assess how tightly bound the enzymes are to the particles. The results of the soil pore water assays showed little to no enzyme activity (&lt;0.05 nmol g soil–1 h–1), suggesting that enzymes are not abundant in soil pore water. In the soil cores, we detected activity for most of the hydrolytic enzymes, and there were clear differences among the particle size and disruption treatments. Higher activities in unfiltered and 50-µm filters relative to much finer 2-µm filters suggested that the enzymes were preferentially associated with larger particles in the soil, likely the organic material that makes up the bulk of these Arctic soils. Furthermore, in the sonication + blending treatment with no filter, 5 of 6 hydrolytic enzymes showed higher activity compared to blending only (and much higher than sonication only), further indicating that enzyme–substrate complexes throughout the organic matter component of the soil matrix are the sites of hydrolytic enzyme activity. These results suggest that the enzymes are likely bound to either the producing microbes, which are bound to the substrates, or directly to the larger organic substrates they are decomposing. This close-proximity binding may potentially minimize the transport of decomposition products away from the microbes that produce them.

Bracken Growth, Toxin Production and Transfer From Plant to Soil - A Two-year Monitoring Study

Background: Bracken fern (Pteridium aquilinum) is known to produce several toxic glycosides, of which ptaquiloside (PTA) is the most well documented. PTA may release from bracken to soil and leach to surface and groundwater. This study presents the first comprehensive long-term (2018-2019) monitoring study of bracken biomass, PTA content in the biomass, release by precipitation and soil solution concentrations at 50 cm depth. Moreover, lab experiments were carried to estimate the degradation of PTA, for different soil horizons and moisture contents. Results: The PTA content in bracken was highest at the beginning of the season, following a decreasing trend towards negligible values at the end of the season. The maximum seasonal PTA mass in the canopy was observed early in the summer, with values up to 1600 mg m-2. PTA is washed in high amounts by precipitation, with releases of up to 13.1 mg PTA m-2 during a single rain event. Concentrations of PTA in soil pore water were positively correlated with the mass of PTA in the canopy during the growing season. Peak concentrations of PTA in the soil solution were observed in July, with an average concentration of 1050 ng L-1.Conclusions: The production of PTA in bracken was found to be proportional to biomass production, while the mass of PTA being released is a function of volume and intensity of precipitation, as well as the bracken canopy development stage. Leaching of PTA takes place in the form of pulses linked to precipitation events, with soil pore water concentrations exceeding levels which are known to pose a risk to human health.