Hydrologic Modifications Challenge Bottomland Hardwood Forest Management

Bottomland hardwoods are floodplain forests along rivers and streams throughout the southeastern United States. The interrelations among hydrology, soils, geomorphic landforms, and tree species composition are the foundation of forest management in bottomland hardwoods, and historically their correspondence has allowed for somewhat predictable forest responses based upon the hydrogeomorphic setting. However, extensive hydrologic and geomorphic modifications in floodplains have disrupted these interrelations and, on many sites, have created novel disturbance regimes resulting in unpredictable forest responses. Reduced or altered timing of surface flooding and groundwater declines are common in the region and have favored increases in stem densities, particularly of species less tolerant of flooding and more tolerant of shade. In these highly modified systems, more process-level understanding of floodplain hydrology, soil moisture dynamics, interspecific tree competition, and regeneration is needed to develop more effective management prescriptions and for forestry to be represented in integrated water-resource management decisions.

The long-term impacts of forest removal on floodplain subsurface hydrology

A study was implemented in fall 2010, in the Hinkson Creek Watershed, Missouri, USA to improve quantitative understanding of the long-term impact of forest removal on floodplain hydrology. Automated volumetric water content (VWC) probes and piezometers equipped with pressure transducers to monitor shallow groundwater (SGW) temperature and level were installed in a gridded study design within a historic agricultural field (Ag) and a remnant bottomland hardwood forest (BHF). Groundwater was analyzed for 49 physiochemical metrics. Results showed VWC to be significantly different between sites (p less than 0.01) during the study, with site averages of 33.1 and 32.8% at the Ag and BHF sites, respectively. Semi-variogram analyses results suggest historic forest removal and cultivation of the Ag site facilitated the development of strong VWC spatial dependency. SGW temperature range at the Ag site was 72% greater than at the BHF site. BHF groundwater contained significantly (p less than 0.05) higher concentrations of nutrients, while Ag groundwater was characterized by significantly (p less than 0.05) higher concentrations of trace elements. Collective results highlight the greater extent to which BHF vegetation impacts subsurface hydrology, relative to grassland/agricultural systems, and point to the value of reestablishing floodplain forests for freshwater routing, water quality, aquatic ecosystem conservation, and flood mitigation in mixed-land-use watersheds.

Dissolved oxygen and water temperature dynamics in lowland rivers over various timescales

The impact of floodplain hydrology on the in-stream dissolved oxygen dynamics and the relation between dissolved oxygen and water temperature are investigated. This has been done by examining the time series of dissolved oxygen and water temperature coupled with meteorological and hydrological data obtained from two lowland rivers having contrasting hydrological settings. Spectral analysis of long-term oxygen variations in a vegetated river revealed a distinct scaling regime with slope ‘–1’ indicating a self-similar behaviour. Identical slopes were obtained for water temperature and water level. The same power-law behaviour was observed for an unvegetated river at small timescales revealing the underlying scaling behaviour of dissolved oxygen regime for different types of rivers and over various time scales. The results have shown that the oxygenation of a vegetated river is strongly related to its thermal regime and flow conditions. Moreover, analysis of short-term fluctuations in the unvegetated river demonstrated that physical factors such as rainfall and backwaters play a substantial role in the functioning of this ecosystem. Finally, the results show that the relation between water temperature and dissolved oxygen concentration at the diurnal timescale exhibits a looping behaviour on the variable plot. The findings of this study provide an insight into the sensitivity of rivers to changing hydro-physical conditions and can be useful in the assessment of environmental variability.

Beccles Triple Post Alignment, Beccles Marshes, Suffolk: Excavation and Palaeoenvironmental Analyses of an Iron Age Wetland Site

This paper describes the results of two seasons of excavation and associated palaeoenvironmental analyses of a wetland site on Beccles Marshes, Beccles, Suffolk. The site has been identified as a triple post alignment of oak timbers (0.6–2.0 m long), over 100 m in length, and 3–4 m wide, running north-west to south-east towards the River Waveney. It was constructed in a single phase which has been dated dendrochronologically to 75 BC, although discrete brushwood features identified as possible short trackways have been dated by radiocarbon to both before and after the alignment was built. It is unclear if the posts ever supported a superstructure but notches (‘halving lap joints’) in some of the posts appear to have held timbers to support the posts and/or aid in their insertion. In addition, fragments of both Iron Age and Romano-British pottery were recovered. A substantial assemblage of worked wooden remains appears to reflect the construction of the post row itself and perhaps the on-site clearance of floodplain vegetation. This assemblage also contains waste material derived from the reduction splitting of timbers larger than the posts of the alignment, but which have not been recovered from the site. Environmental analyses indicate that the current landscape context of the site with respect to the River Waveney is probably similar to that which pertained in prehistory. The coleoptera (beetle) record illustrates a series of changes in the on-site vegetation in the period before, during and after the main phase of human activity which may be related to a range of factors including floodplain hydrology and anthropogenic utilisation of Beccles Marshes. The possible form and function of the site is discussed in relation to the later prehistoric period in Suffolk.