Wildfire impacts on freshwater detrital food webs depend on runoff load, exposure time and burnt forest type

2020

Land Degrad Dev

Land degradation and water resources pollution caused by catastrophic wildfires is of growing concern in fire‐prone regions. Studies on the effects of wildfire on hydrology and erosion have mostly been conducted at plot or hillslope scale, while relatively few studies investigated post‐wildfire hydrological responses and erosion at the meso‐catchment scale (~ > 10 km2) in the Mediterranean. This study used measured discharge and suspended sediment at the outlet of a burnt catchment in southern Portugal, before and after a wildfire, to investigate post‐wildfire changes in hydrological and erosion responses to rainfall. Hydrological and sediment connectivity patterns were derived to investigate changing dynamics induced by the fire within the catchment. The main findings were: (a) although a large part of the catchment experienced moderate to high severity burning, post‐wildfire hydro‐sedimentary response was considerably limited; (b) meteorological variability determined hydrological responses and erosion more strongly than wildfire effects; and (c) during the post‐wildfire vegetation recovery period, only rainfall events with a high return period (~ 2 years) enhanced the hydrological and erosion responses. This can be explained by the spatial scale dependency of these processes and limited fine sediment supply, or relatively low connectivity in the study catchment. While connectivity is only an indicator, this implies that, at the meso‐catchment scale, pollution of downstream water bodies by contaminated soil and ash may not occur immediately. Rather, because sediments and associated ashes and contaminants are first being transported to the areas around the stream networks, they only reach the outlet during heavy events which do connect the entire catchment. Thus, dynamic indices of connectivity that take rainfall event characteristics into consideration need to be further tested to assess and manage post‐wildfire soil and water contamination risk.

Section: Discussionmentioning

confidence: 70%

Comparing the impacts of wildfire and meteorological variability on hydrological and erosion responses in a Mediterranean catchment

2020

Land Degrad Dev

“…The fire appeared to lead to a large increase in sediment supply, decreasing the importance of sediment limitations in favour of transport limitations, and changing sediment yield patterns. It is possible that the normal sediment yield patterns in agroforestry headwater catchments have peak sediment yields during the autumn harvest and ploughing season, as observed for Macieira (Figure 3c (Campos, Abrantes, Keizer, Vale, & Pereira, 2016;Carvalho et al, 2019;Silva et al, 2015). Sediments accumulated in stream networks, as was the case in Macieira (Figure 3e), have the potential for long-term impacts on water quality.…”

Section: Implications For the Role Of Fires On Hydrological And Sedmentioning

confidence: 88%

“…It is worth stressing that the excess in sediment supply following the fire occurred despite the relatively small size of the burnt area and a relatively high streamflow, at least during the second post‐fire year (2012/2013). Even limited fire‐induced sediment supply could have a negative impact on downstream aquatic ecosystems and organisms, as they are sensitive to the toxic compounds present in ashes and burnt topsoil (Campos, Abrantes, Keizer, Vale, & Pereira, 2016; Carvalho et al, 2019; Silva et al, 2015). Sediments accumulated in stream networks, as was the case in Macieira (Figure 3e), have the potential for long‐term impacts on water quality.…”

Section: Discussionmentioning

confidence: 99%

Impacts of wildfire and post‐fire land management on hydrological and sediment processes in a humid Mediterranean headwater catchment

Bernard-Jannin

Rodríguez‐Blanco

et al. 2020

Hydrological Processes

Self Cite

The extensive afforestation of the Mediterranean rim of Europe in recent decades has increased the number of wildfire disturbances on hydrological and sediment processes, but the impacts on headwater catchments is still poorly understood, especially when compared with the previous agricultural landscape. This work monitored an agroforestry catchment in the northwestern Iberian Peninsula, with plantation forests mixed with traditional agriculture using soil conservation practices, for one year before the fire and for three years afterwards, during which period the burnt area was ploughed and reforested. During this period, continuous data was collected for meteorology, streamflow and sediment concentration at the outlet, erosion features were mapped and measured after major rainfall events, and channel sediment dynamics were monitored downstream from the agricultural and the burnt forest area. Data from 202 rainfall events with over 10 mm was analysed in detail. Results show that the fire led to a notable impact on sediment processes during the first two post-fire years, but not on streamflow processes; this despite the small size of the burnt area (10% of the catchment) and the occurrence of a severe drought in the first year after the fire. During this period, soil loss at the burnt forest slopes was much larger than that at most traditionally managed fields, and, ultimately, led to sediment exhaustion. At the catchment scale, storm characteristics were the dominant factor behind streamflow and sediment yield both before and after the fire. However, the data indicated a shift from detachment-limited sediment yield before the fire, to transport-limited sediment yield afterwards, with important increases in streamflow sediment concentration. This indicates that even small fires can temporarily change sediment processes in agroforestry catchments, with potential negative consequences for downstream water quality.

“…It is worth stressing that the excess in sediment supply following the fire occurred despite the relatively small size of the burnt area and a relatively high streamflow, at least during the second postfire year (2012/13). Even limited fire-induced sediment supply could have a negative impact on downstream aquatic ecosystems and organisms, as they are sensitive to the toxic compounds present in ashes and burnt topsoil (Silva et al, 2015;Campos et al, 2016;Carvalho et al, 2019). Sediments accumulated in stream networks, as was the case in Macieira (Figure 3e), have the potential for longterm impacts on water quality.…”

Section: Implications For the Role Of Fires On Hydrological And Sediment Processesmentioning

confidence: 99%

Impacts of wildfire and post-fire land management on hydrological and sediment processes in a humid Mediterranean headwater catchment

Bernard-Jannin

Rodríguez‐Blanco

et al. 2021

Preprint

Self Cite

<p>The extensive afforestation of the Mediterranean rim of Europe in recent decades has increased the number of wildfire disturbances on hydrological and sediment processes, but the impacts on headwater catchments is still poorly understood, especially when compared with the previous agricultural landscape. This work monitored an agroforestry catchment in the north-western Iberian Peninsula, with plantation forests mixed with traditional agriculture using soil conservation practices, for one year before the fire and for three years afterwards, during which period the burnt area was plowed and reforested. During this period, continuous data was collected for meteorology, streamflow and sediment concentration at the outlet, erosion features were mapped and measured after major rainfall events, and channel sediment dynamics were monitored downstream from the agricultural and the burnt forest area. Data from 202 rainfall events with over 10 mm was analysed in detail.</p><p>Results show that the fire led to a notable impact on sediment processes during the first two post-fire years, but not on streamflow processes; this despite the small size of the burnt area (10% of the catchment) and the occurrence of a severe drought in the first year after the fire. During this period, soil loss at the burnt forest slopes was much larger than that at most traditionally managed fields, and, ultimately, led to sediment exhaustion. At the catchment scale, storm characteristics were the dominant factor behind streamflow and sediment yield both before and after the fire. However, the data indicated a shift from detachment-limited sediment yield before the fire, to transport-limited sediment yield afterwards, with important increases in streamflow sediment concentration. This indicates that even small fires can temporarily change sediment processes in agroforestry catchments, with potential negative consequences for downstream water quality.</p>