Samia Richards

Relationships between Soil Physicochemical, Microbiological Properties, and Nutrient Release in Buffer Soils Compared to Field Soils

The retention of nutrients in narrow, vegetated riparian buffer strips (VBS) is uncertain and underlying processes are poorly understood. Evidence suggests that buffer soils are poor at retaining dissolved nutrients, especially phosphorus (P), necessitating management actions if P retention is not to be compromised. We sampled 19 buffer strips and adjacent arable field soils. Differences in nutrient retention between buffer and field soils were determined using a combined assay for release of dissolved P, N, and C forms and particulate P. We then explored these differences in relation to changes in soil bulk density (BD), moisture, organic matter by loss on ignition (OM), and altered microbial diversity using molecular fingerprinting (terminal restriction fragment length polymorphism [TRFLP]). Buffer soils had significantly greater soil OM (89% of sites), moisture content (95%), and water-soluble nutrient concentrations for dissolved organic C (80%), dissolved organic N (80%), dissolved organic P (55%), and soluble reactive P (70%). Buffer soils had consistently smaller bulk densities than field soils. Soil fine particle release was generally greater for field than buffer soils. Significantly smaller soil bulk density in buffer soils than in adjacent fields indicated increased porosity and infiltration in buffers. Bacterial, archaeal, and fungal communities showed altered diversity between the buffer and field soils, with significant relationships with soil BD, moisture, OM, and increased solubility of buffer nutrients. Current soil conditions in VBS appear to be leading to potentially enhanced nutrient leaching via increasing solubility of C, N, and P. Manipulating soil microbial conditions (by management of soil moisture, vegetation type, and cover) may provide options for increasing the buffer storage for key nutrients such as P without increasing leaching to adjacent streams.

Assessment of the use of sediment fences for control of erosion and sediment phosphorus loss after potato harvesting on sloping land

In humid temperate areas, after harvest of potatoes, it is difficult to prevent soil erosion and diffuse pollution. In some autumn weather conditions, in-field mitigation such as cultivation or sowing are not possible, while edge of field measures can be costly and inflexible. We have assessed the potential of modified sediment fences, widely used on building sites, for erosion mitigation post-harvest of potato crops. Field scale assessments were conducted on fields in the Lunan catchment, eastern Scotland. Sediment retention was estimated by two methods: a topographic survey method using a hand held Real Time Kinematic Global Positioning System (RTK-GPS), and direct measurement of sediment depth using a graduated cane. In the 2010/11 trial the main fence comprised 70 m of entrenched fine mesh (0.25 mm) and coarser mesh (4mm) fabric pinned to a contour fence near the base of the field. This retained an estimated 50.9 m(3) (80.2 tonnes) of sediment, with weighted mean total P (TP) content of 0.09 % in the<2mm soil fraction. In the 2011/12 trial, the main 146 m fence was of intermediate mesh size (1.2mm). The fence was partitioned into nine upslope plots, with 3 replicates of each of 3 cultivation methods: T1 (full grubbing--a light, tined cultivator), T2 (partial grubbing) and T3 (no grubbing). Average plot slopes ranged from 9.9 to 11.0 %. The amounts of TP accumulating as sediment at the fences were: 9.3 (sd = 7.8), 11.8 (sd = 10.2) and 25.7 (sd = 5.8)kg P/ha of upslope plot for the T1, T2 and T3 treatments respectively.

Temporal variability in domestic point source discharges and their associated impact on receiving waters.

Discharges from the widely distributed small point sources of pollutants such as septic tanks contribute to microbial and nutrient loading of streams and can pose risks to human health and stream ecology, especially during periods of ecological sensitivity. Here we present the first comprehensive data on the compositional variability of septic tank effluents (STE) as a potential source of water pollution during different seasons and the associated links to their influence on stream waters. To determine STE parameters and nutrient variations, the biological and physicochemical properties of effluents sampled quarterly from 12 septic tank systems were investigated with concurrent analyses of upstream and downstream receiving waters. The study revealed that during the warmer dryer months of spring and summer, effluents were similar in composition, as were the colder wetter months of autumn and winter. However, spring/summer effluents differed significantly (P<0.05) from autumn/winter for concentrations of biological oxygen demand (BOD), arsenic, barium (Ba), cobalt, chromium, manganese, strontium (Sr), titanium, tungsten (W) and zinc (Zn). With the exception of BOD, Ba and Sr which were greater in summer and spring, the concentrations of these parameters were greater in winter. Receiving stream waters also showed significant seasonal variation (P≤0.05) in alkalinity, BOD, dissolved organic carbon, sulphate, sulphur, lithium, W, Zn and Escherichiacoli abundance. There was a clear significant influence of STE on downstream waters relative to upstream from the source (P<0.05) for total suspended solids, total particulate P and N, ammonium-N, coliforms and E. coli. The findings of this study found seasonal variation in STE and place effluent discharges as a factor affecting adjacent stream quality and call for appropriate measures to reduce or redirect STE discharges away from water courses.

The potential use of natural vs commercial biosorbent material to remediate stream waters by removing heavy metal contaminants

The presence of high level of heavy metals in aquatic environment is a cause of ecological and environmental concern and thus their removal from water courses is environmentally essential. Four natural inexpensive biosorbents: macro algae (Fucus vesiculosus), crab shells (Cancer pagurus), wood chippings and iron-rich soil were tested for copper (Cu2+) and zinc (Zn2+) removal from aqueous solutions. Batch equilibrations were performed at 1:100 w/v with different initial metal concentrations. Three macro algae pre-treatments (unmodified (UM algae), chemically treated (Ca-T algae) and thermally treated (T-T algae)) were additionally investigated for performance. The sorption capacities were compared with the commercial material biochar and activated carbon. The maximum level of the sorbents for Cu2+ uptake at 15.7 mM/l was attained by the natural material of UM algae (72.37 ± 0.37 mg/g) > Ca-T algae (66.77 ± 0.19 mg/g) > T-T algae (63.06 ± 0.82 mg/g), followed by the commercial material activated carbon (36.71 ± 2.20 mg/g). The maximum level of the sorbents for Zn2+ uptake at 15.3 mM/l was also achieved by the natural material of UM algae (52.40 ± 0.80 mg/g) > Ca-T algae (48.83 ± 2.01 mg/g) > T-T algae (39.57 ± 0.80 mg/g) followed by the commercial material activated carbon (20.78 ± 1.63 mg/g) and biochar (18.07 ± 1.09 mg/g). The results demonstrated that Cu2+ and Zn2+ were effectively removed by these biosorbents at all concentrations. However, at high metals concentrations, the natural material macro algae had greater Cu2+ and Zn2+ sorption capacity than the conventional sorbent activated carbon, and the affinity of these natural biosorbents were greater for Cu2+ than Zn2+. Hence, inexpensive natural and readily available materials showed potential as biosorbents to remediate polluted stream water of toxic metal contaminants.