Terrestrial ecosystems contribute many different forms of organic matter to adjacent waterbodies. Carbon, nitrogen, and phosphorus in this material can significantly influence the planktonic communities of these systems, especially where there is a large proportion of contributing area relative to waterbody size and where nutrients are generally in short supply. Plant pollen, which upon degradation releases nutrients into the water column, is one such source of allochthonous material. In Cape Cod (Massachusetts, USA), large amounts of pollen from dense pitch pine (Pinus rigida L.) forest are deposited in late spring into small, freshwater lakes scattered across the landscape. This study examines in vivo chlorophyll fluorescence responses of surface-water samples collected from three such lakes within Cape Cod National Seashore (Wellfleet and Truro) to additions of P. rigida pollen in a laboratory setting. The results indicate that where influxes are high enough, pollen can have a stimulatory effect on phytoplankton communities and is a short-term nutrient subsidy in these systems at a time of year (May-June) when warming temperatures and faster growth rates elevate the demand for nutrients. 相似文献
This study focuses on characterizing the thermoluminescence (TL) and optically stimulated luminescence (OSL) of quartz in burnt clay, pottery, and the sediments unearthed from a Neolithic site, the Beicun site of the Liangzhu culture. It shows that the initial OSL signals (within 0.8 s) of most burnt clay and pottery sherds are not dominated by the fast component. Results of a heating simulation experiment of sediment quartz show that annealing at temperatures exceeding 600–800 °C decreased the proportion of the fast component in the initial signal slightly. In addition, the proportion of the medium component in the later signal (0.8–5 s) increased significantly, resulting in a decrease in the Fast Ratio value. Therefore, high annealing temperature may be an important reason for the slow decay rate of OSL signals of the burnt clay and pottery samples. The De(t) plot shows that most of the samples have thermally stable OSL component signals, which have no significant effect on the final OSL ages. The single-aliquot regenerative-dose (SAR) protocol was used to determine the OSL and TL ages for chunk burnt clay and pottery sherds. The high-precision age of the last archaeological heating event, such as sacrifice, burning, or domestic firing, can be obtained by determining the TL and OSL ages of a homogeneous chunk of burnt clay. The OSL results are consistent with the 14C age of carbon chips extracted from burnt clay. The age of the Beicun site is finally determined to be approximately 5000–5300 BP (BP represents before 2020), belonging to the early period of the Liangzhu culture. 相似文献
