Towards sustainable management of polyacrylamide in soil-water environment: Occurrence, degradation, and risk.

Polyacrylamide (PAM) possesses unique characteristics, including high water solubility, elevated viscosity and effective flocculation capabilities. These properties make it valuable in various sectors like agriculture, wastewater treatment, enhanced oil recovery, and mineral processing industries, contributing to a continually expanding market. Despite its widespread use globally, understanding its environmental fate at the soil-water interface remains limited. This article aims to provide an overview of the occurrence, degradation pathways, toxicity, and risks associated with PAM in the bioenvironment. The findings indicate that various degradation pathways of PAM may occur in the bioenvironment through mechanical, thermal, chemical, photocatalytic degradation, and/or biodegradation. Through a series of degradation processes, PAM initially transforms into oligomers and acrylamide (AM). Subsequently, AM may undergo biodegradation, converting into acrylic acid (AA) and other compounds such as ammonia. Notably, among these degradation intermediates, AM demonstrates high biodegradability, and the bioaccumulations of both AM and AA are not considered significant. Ensuring the sustainable use of PAM necessitates a comprehensive understanding among policymakers, scholars, and industry professionals regarding PAM, encompassing its properties, applications, degradation pathways, toxic effect on humans and the environment, and relevant regulations. Additionally, this study offers insights into future priority research directions, such as establishing of a reliable source-to-destination supply chain system, determining the maximum allowable amount for PAM in farmlands, and conducting long-term trials for the PAM-containing demolition residues.

Responses of a common tropical epiphyte, Asplenium nidus, to changes in water and nutrient availability.

Epiphytes are highly dependent on atmospheric inputs of water and nutrients. Reductions in water availability associated with warming and climate change and continual atmospheric nitrogen (N) deposition can affect plant growth but few studies have evaluated the effects of changes in both water and nutrient availabilities on epiphytes. We experimentally tested whether epiphyte growth is more water- or nutrient-limited, if nutrient limitation was stronger for nitrogen or phosphorus, and whether nutrient limitation interacts with water availability. We applied watering (high and low) and nutrient addition (control, +N, +P, +N+P) treatments to greenhouse-grown Asplenium nidus, a common epiphytic fern found in many tropical and subtropical wet forests. We measured leaf area production and leaf elemental concentrations to assess how A. nidus growth and physiology respond to changes in water and nutrient availabilities. We found that leaf growth of A. nidus was more affected by water availability than nutrient addition and the effect of adding nutrients was not fully realized under low-water availability. Among the different nutrient treatments, +N+P had the greatest effects on A. nidus growth and physiology in both watering treatments. Watering treatment changed leaf elemental concentrations but not their ratios (i.e. C:N and N:P). Nutrient addition altered C:N and N:P ratios and increased the concentration of the added elements in leaves, with more pronounced increases in the high-watering treatment. We conclude that the growth of A. nidus is more water- than nutrient-limited. When nutrient limitation occurs (i.e. under high-water availability), nutrient co-limitation is stronger than limitation by N or P alone. This result taken together with studies of other epiphytes suggests greater water than nutrient limitation is likely widespread among epiphytic plants. The limited effects of nutrient addition in the low-water treatment suggest that the effect of atmospheric N deposition on epiphyte growth will be limited when water availability is low.

Trends of two decadal precipitation chemistry in a subtropical rainforest in East Asia.

Long-term monitoring of precipitation chemistry provides a great opportunity to examine the evolution of air pollutant emissions and effectiveness of air pollution control measures. We evaluated the characteristics and trends of precipitation chemistry at both annual and seasonal scales based on the records of 1994-2013 at Fushan Experimental Forest (FEF) of northeastern Taiwan. The results showed that 77% of the weekly precipitation had pH<5.0. The two-decadal average annual pH was 4.62, without a significant inter-annual trend, possibly due to the concurrent declines of both acidic pollutants and base cations. There was a significant positive relationship between [SO42-+NO3-] and [Ca2++NH4+] indicating that their deposition was likely dominated by NH4NO3, (NH4)2SO4, Ca(NO3)2, and CaSO4. There was a significant negative relationship between precipitation pH and the difference between [SO42-+NO3-] and [Ca2++NH4+], not just [SO42-+NO3-], suggesting that precipitation acidity was not solely determined by acidic pollutants but by the balance between acidic pollutants and base cations. We also found temporal decreases of Ca2+ and NH4+ concentrations in precipitation which contributed to the low acid neutralization capacity of precipitation. Annual deposition of NO3- and SO42- was 23 and 55kgha-1yr-1, which is much higher than most forest sites in the industrialized countries suggesting that acid deposition is still a major environmental issue in Taiwan. Annual deposition of NH4+, Ca2+ and NO3- showed significant decreasing trends during the 20-year period, which was mostly due to the decreases in the summer deposition associated with air pollution mitigation strategies. Winter deposition showed no decreasing patterns for the same period. The high contribution to annual acid deposition from autumn-winter and spring rains (50%) associated with northeast monsoon implies that long-range transport of anthropogenic emissions from East Asia played a key role on acid depositions at FEF and possibly many areas in the region. Therefore, intergovernmental cooperation is urgently needed to effectively mitigate the threat of acid deposition in East Asia.

Modeling the terrestrial N processes in a small mountain catchment through INCA-N: A case study in Taiwan.

Riverine dissolved inorganic nitrogen (DIN) is an important indicator of trophic status of aquatic ecosystems. High riverine DIN export in Taiwan, ~3800kg-Nkm-2yr-1, which is ~18 times higher than the global average, urges the need of thorough understanding of N cycling processes. We applied INCA-N (Integrated Nitrogen Catchment Model) to simulate riverine DIN export and infer terrestrial N processes using weekly rainwater and streamwater samples collected at the Fushan Experimental Forest (FEF) of northern Taiwan. Results showed that the modeled discharge and nitrate export are in good agreement with observations, suggesting the validity of our application. Based on our modeling, the three main N removal processes, in the order of descending importance, were plant uptake, riverine N transport and denitrification at FEF. The high plant uptake rate, 4920kg-Nkm-2yr-1, should have led to accumulation of large biomass but biomass at FEF was relatively small compared to other tropical forests, likely due to periodic typhoon disruptions. The low nitrate concentration but high DIN export highlights the importance of hydrological control over DIN export, particularly during typhoons. The denitrification rate, 750kg-Nkm-2yr-1, at FEF was also low compared to other tropical forest ecosystems, likely resulting from quick water drainage through the coarse-loamy top soils. The high DIN export to atmospheric deposition ratio, 0.45, suggests that FEF may be in advanced stages of N excess. This simulation provides useful insights for establishing monitoring programs and improves our understanding N cycling in subtropical watersheds.

Ecological facilitation between two epiphytes through drought mitigation in a subtropical rainforest.

Positive species interactions (facilitation) play an important role in shaping the structures and species diversity of ecological communities, particularly under stressful environmental conditions. Epiphytes in rainforests often grow in multiple-species clumps, suggesting interspecies facilitation. However, little is known about the patterns and mechanisms of epiphyte co-occurrence. We assessed the interactions of two widespread epiphyte species, Asplenium antiquum and Haplopteris zosterifolia, by examining their co-occurrence and size-class association in the field. To elucidate factors controlling their interactions, we conducted reciprocal-removal and greenhouse-drought experiments, and nutrient and isotope analyses. Forty-five percent of H. zosterifolia co-occurred with A. antiquum, whereas only 17% of A. antiquum co-occurred with H. zosterifolia. Removing the fronds plus substrate of A. antiquum reduced the relative frond length and specific leaf area of H. zosterifolia, but removing fronds only had little effect. Removing H. zosterifolia had no significant effects on the growth of A. antiquum. H. zosterifolia co-occurring and not co-occurring with A. antiquum had similar foliar nutrient concentrations and δ(15)N values, suggesting that A. antiquum does not affect the nutrient status of H. zosterifolia. Reduced growth of H. zosterifolia with the removal of A. antiquum substrate, together with higher foliar δ(13)C for H. zosterifolia growing alone than those co-occurring with A. antiquum, suggest that A. antiquum enhances water availability to H. zosterifolia. This enhancement probably resulted from water storage in the substrate of A. antiquum, which could hold water up to 6.2 times its dry weight, and from reduced evapotranspiration due to shading of A. antiquum fronds. Greater water loss occurred in the frond-clipped group than the unclipped group between days 3-13 of the drought treatment. Our results imply that drought mitigation by substrate-forming epiphytes is important for maintaining epiphyte diversity in tropic and subtropic regions with episodic water limitations, especially in the context of anthropogenic climate change.

Fog and precipitation chemistry at a mid-land forest in central Taiwan.

We analyzed fog and bulk precipitation chemistry at a cloud forest in central Taiwan where mountain agriculture activities are highest. There were 320 foggy days (visibility <1000 m) recorded between April 2005 and March 2006. Fog was most frequent between April 2005 and July 2005 and in March 2006 (153/153 d) and least frequent in January 2006 (21/31 d). The total fog duration was 2415 h, representing 28% of the sampling period. Compared with bulk precipitation, fog was disproportionally enriched in NO(3)(-) and SO(4)(2-) relative to K(+), Ca(2+), Mg(2+), and NH(4)(+), resulting in higher a content of nitric acid and sulfuric acid than weak acids or neutral salts and, therefore, higher acidity (median pH, 4.9) in fog than in bulk precipitation (median and mean pH, 5.5). The very high input of NH(4)(+) (47 kg N ha(-1) yr(-1)) through bulk precipitation suggests that the use of fertilizer (ammonium sulfate and animal manure) associated with mountain agriculture has a major impact on atmospheric deposition at the surrounding forest ecosystems. The input of inorganic N reached 125 kg N ha(-1) yr(-1) and likely exceeded the biological demand of the forest ecosystem. Sulfate is the most abundant anion in fog at Chi-tou and in precipitation at various forests throughout Taiwan, suggesting that the emission and transport of large quantities of SO(2,) the precursor of SO(4)(2-), is an island-wide environmental issue.