Wildfire impacts on hillslope sediment and phosphorus yields

Abstract

Purpose The impact of wildfire on (a) slope hydrological processes, (b) soil erodibility, and (c) post-fire hillslope sediment and phosphorus (P; dissolved and particulate) yields are quantified for natural forest areas of the burned Evrotas River basin, Peloponnese, Greece. Further, the geochemical partitioning of P in burned and unburned sediment is evaluated by sequential extraction to assess potential bioavailability of particulate P (PP) in downstream aquatic ecosystems. Materials and methods A series of field-based rainfall simulation and infiltration experiments were undertaken in burned and unburned terrain of contrasting vegetation and soil type, after severe wildfires in summer 2007. Resulting water and sediment samples were analyzed for P concentration to permit calculation of hillslope yields for 20, 40, and 60 mm h -1 rainfall events. Samples of soil were collected from each site type for physical and geochemical analyses.Results and discussion Plot-scale rainfall simulation experiments and measurements demonstrate enhanced runoff and erosion rates in burned terrain. While dissolved P concentrations in runoff from burned terrain are elevated (0.21± 0.09 mg l -1 ) against background levels (0.01±0.01 mg l -1 ) and exceed European water quality guidelines, PP represents 99% of the severely burned hillslope P yield (2.32± 1.63 kg ha -1 for a 15-min rainfall event). Sequential extraction data demonstrate that up to 20% of total PP in burned sediment is potentially bioavailable and that bioavaliable PP yields are two orders of magnitude greater than dissolved P yields. Conclusions Release of P from eroded sediment stored in downslope/downstream sink zones may protract the postfire risk to downstream resources. Quantification of PP partitioning in eroded sediment is a key requirement when assessing the downstream impacts of wildfire.

Non-perennial Mediterranean rivers in Europe: Status, pressures, and challenges for research and management

“…Wildfires, which frequently occur during periods of extended drought, pose another major risk for NPRS. Initial floods following wildfires enhance runoff and erosion rates in burned terrains, causing elevated sediment and phosphorus concentrations in receiving downstream water bodies (Blake et al, 2010). Finally, studies that focused on the relative vulnerability of PRS and NPRS to anthropogenic stress have shown that habitat changes (García-Roger et al, 2011) and agro-industrial pressures ) exert severe effects on aquatic macroinvertebrates in NPRS, more severe than in comparable PRS.…”

Impacts of Wildfire Severity on Hydraulic Conductivity in Forest, Woodland, and Grassland Soils

“…K sat reductions of 20 to 48% are commonly reported (Table 3). Blake et al (2009) also noted K sat reductions of 88 to 92% with high severity wildfire. An interesting trend emerging out of some of the recent Australian research on the impacts of wildfires on soil hydrologic properties including K sat is that the soil surface K sat values can be similar regardless of severity (Rab 1996 andNyman et al 2011) and that natural water repellency may produce K sat values less than those measured in burned soils (Sheridan et al2007).…”

“…One clear signature of K sat parameters is that they are highly variable (Doerr et al 1998, Doerr et al 2006. A number of recent studies reporting changes in K sat listed in Table 3 demonstrate clear reductions in conductivity after fires (Parks & Cundy 1989, Greene et al 1990, Robichaud 2000, Ekinci 2006, Fox et al 2007, Ekinci et al 2008, Blake et al 2009, Novák et al 2009, and Nyman et al 2011. Fire severity plays a key role in some of these reductions, but other investigators have demonstrated a surprising lack of correlation with severity (Rab 1996, Valzano et al 1997, Sheridan et al 2007, and Blake et al 2009.…”

Sediment response to catchment disturbances

“…In the set of conditions sampled, the upstream effects of cattle and road erosion result in larger stream turbidity responses than the areas harvested with stream side buffers. Blake et al (2010) show how severe wildfires in Greece increased sediment mobilization and yields on hillslopes. Importantly, they also demonstrated that the wildfires not only increased the particulate phosphorus delivery from hillslopes to receiving river channels but that the bioavailability of P in the mobilized sediment also increased due to the wildfires, which could pose a long-term threat to aquatic ecosystems.…”