Comparison of production computation methods in a Southeastern North CarolinaSpartina alterniflora salt marsh

Tagging studies ofSpartina alterniflora Loisel showed no significant differences in stem longevity of short, medium, and tall height forms. Mean stem longevity was 7.9 months, and the experimental turnover rate was 1.5 crops per yr. Five methods to measure productivity (peak standing crop, Milner and Hughes, Smalley, Wiegert and Evans, and Lomnicki, et al.) yielded annual net aerial primary production (NAPP) estimates ranging from 214 to 1,038 g dry wt per m² per yr in a stand of shortSpartina. Turnover rates were computed for each of the methods by dividing the respective production value by the peak standing crop (242 g dry wt per m² per yr). Each computed turnover rate was compared with the experimental value of 1.5 crops per yr to ultimately determine that the methods of peak standing crop, Milner and Hughes, and Smalley were underestimates and that the Wiegert and Evans method was an overestimate of NAPP in tidal marsh systems. Based on its calculated turnover rate of 1.9 crops per yr, a modified Lomnicki, et al. method provided the best NAPP estimate (454 g dry wt per m² per yr).     

Taphonomy and site formation on California's Channel Islands

Inhabited by humans for over 12,000 calendar years, California's Channel Islands contain thousands of archaeological sites, ranging from dense shell middens and villages to small lithic scatters and camps. Similar to many islands around the world, the Channel Islands have a dearth of burrowing animals and limited historical development leading to generally good preservation of archaeological constituents and relatively high stratigraphic integrity. Despite these favorable preservation conditions, numerous natural and cultural processes have impacted the island's archaeological record. Channel Islands archaeologists, however, have given relatively limited attention to the effects of taphonomic and formation processes. The authors provide an overview of taphonomic and formation processes affecting Channel Islands archaeology, illustrating the importance of regional taphonomic syntheses in the management, preservation, and interpretation of archaeological sites. These data also demonstrate the significance of detailing formation processes in islands and other areas where burrowing rodents and other disturbances are thought to be absent or limited. © 2006 Wiley Periodicals, Inc.     

Headless submarine canyons and fluid flow on the toe of the Cascadia accretionary complex

Headless submarine canyons with steep headwalls and shallowly sloping floors occur on both the second and third landward vergent anticlines on the toe of the Cascadia accretionary complex off central Oregon (45 °N, 125° 30′W). In September 1993, we carried out a series of nine deep tow camera sled runs and nine ALVIN dives to examine the relationship between fluid venting, structure and canyon formation. We studied four canyons on the second and third landward vergent anticlines, as well as the apparently unfailed intercanyon regions along strike. All evidence of fluid expulsion is associated with the canyons; we found no evidence of fluid flow between canyons. Even though all fluid seeps are related to canyons, we did not find seeps in all canyons, and the location of the seeps within the canyons differed. On the landward facing limb of the second landward vergent anticline a robust cold seep community occurs at the canyon’s inflection point. This seep is characterized by chemosynthetic vent clams, tube worms and extensive authigenic carbonate. Fluids for this seep may utilize high-permeability flow paths either parallel to bedding within the second thrust ridge or along the underlying thrust fault before leaking into the overriding section. Two seaward facing canyons on the third anticlinal ridge have vent clam communities near the canyon mouths at approximately the intersection between the anticlinal ridge and the adjacent forearc basin. No seeps were found along strike at the intersection of the slope basin and anticlinal ridge. We infer that the lack of seepage along strike and the presence of seeps in canyons may be related to fluid flow below the forearc basin/slope unconformity (overpressured by the impinging thrust fault to the west?) directed toward canyons at the surface.     

Sedimentary evidence for recent eutrophication in the northern basin of Lake Taihu,China: human impacts on a large shallow lake

Environmental change in Lake Taihu and its catchment since the early to middle part of the twentieth century has left a clear geochemical record in the lake sediments. The human activities in the lake and its catchment responsible for the change include agriculture, fishery, urbanisation, sewage and industrial waster disposal. Sediment cores were collected from Meilian Bay of northern Lake Taihu to investigate the record of anthropogenic impacts on the lake’s ecosystem and to assess its natural, pre-eutrophication baseline state. Two marked stratigraphic sediment units were identified on the basis of total phosphorus concentration (TP), pigments, total organic carbon (TOC)/total nitrogen (TN), δ¹³C and δ¹⁵N corresponding to stages in the lake history dominated by phytoplankton, and by aquatic macrophytes. Results show that as TP loading increased from the early 1950s the lake produced sediments with increasing amounts of organic matter derived from phytoplankton. In the early 1950s, the first evidence for eutrophication at the Meilian Bay site is recorded by an increase in C/N values and in sediment accumulation rate, but there is little change in phosphorus concentrations, pigments, δ¹³C and δ¹⁵N at this time. After 1990 a more rapid increase in trophic status took place indicated by increased levels of phosphorus, pigments, δ¹⁵N and by decreased δ¹³C and TOC/TN values in the lake sediments. The first increase in trophic status of the early 1950s results mainly from agricultural development in the catchment. In contrast, the acceleration from ca. 1990 originates from the recent development of fisheries and the urbanisation and industrialisation of the catchment.