Open Lake Phosphorus Forcing of Cladophora Growth: Modeling the Dual Challenge in Great Lakes Trophic State Management

Stimulated by excess levels of phosphorus, the attached, filamentous green alga Cladophora grows to nuisance proportions in Lake Michigan, one of the Laurentian Great Lakes. While nearshore waters impacted by local sources of the nutrient continue to support nuisance conditions, offshore waters have undergone oligotrophication in response to reductions in phosphorus loading and benthification of phosphorus cycling by invasive dreissenid mussels. A concept termed the Dual Challenge recognizes that implementation of more stringent phosphorus-loading objectives (to control Cladophora in the nearshore) stands in conflict with a foreseen need to mitigate oligotrophication in the offshore (to sustain a healthy fishery). Attention to this nearshore–offshore dynamic calls into play the role of cross-margin phosphorus transport in mediating both endmembers of the conflict. We applied a biophysical model simulating soluble reactive (SRP) and particulate (PP) phosphorus, mussel biokinetics, and cross-margin mass transport in addressing the Dual Challenge. Pre- and post-dreissenid monitoring results suggest that a reduction in offshore PP levels (food web nutrition) in excess of 40% (2.4 to 1.4 mgP×m−3) has driven oligotrophication and attendant food web dysfunction. Yet, in the absence of local sources, model-predicted nearshore SRP levels remain at or below those required to prevent nuisance growth. These findings indicate that there is a margin of ~1 mgP×m−3 over which offshore PP levels could be increased (to the benefit of the food web and the fishery) without hindering efforts to reduce nuisance algal growth through local source control.

Effects of algae and hydrophytes on the inorganic phosphorus pool of shallow hypereutrophic Lake Taihu

Sedimentary phosphorus is a crucially potential source of phosphorus in the eutrophic lake ecosystem. Different ecological types are supposed to affect the presence and variation of sediment phosphorus. On the basis of field investigations, the total sediment phosphorus load in Zhushan Bay was 1,457.48 mg/kg, nearly four times that of the hydrophyte-dominated area. Thereinto, 41.1% was in the form of iron and aluminum-bound phosphorus, which explicitly indicated the phosphorus contamination there. Analytical methods such as Pearson correlation, contamination assessment and principle component analysis were conducted to find out that ‘contamination’ was not equivalent to ‘release risk’. The contamination classification of East Lake Taihu was ‘clean’ in general. However, 63.3% of the total phosphorus could be mobilized under certain conditions. Therefore, light phosphorus loading does not equal to less release risk. In the long run, the implicit phosphorus release by the activation of organic phosphorus in hydrophytic areas needs close attention. This study provides a reference to understand the influence of hydrophytes and algae on the phosphorus cycle of sediment.

Low Benthic Oxygen and High Internal Phosphorus-Loading are Strongly Associated With the Invasive Macrophyte Nitellopsis obtusa (starry stonewort) in a Large, Polymictic Lake

Lake Scugog is an important headwater to the Trent Severn-Waterway in Ontario, Canada. In recent years, notable ecosystem-level changes have occurred coinciding with the emergence of the non-native invasive charophyte Nitellopsis obtusa. Despite N. obtusa arriving in North America in the early 1970s, studies documenting the impact of N. obtusa on invaded ecosystems are scarce. Given the increasing dominance of N. obtusa in inland waters of the Great Lakes basin, we investigated the ecosystem-level impacts of N. obtusa in Lake Scugog over a 3-year period. We show for the first time a strong association between N. obtusa occurrence and biomass with benthic anoxia in this shallow, polymictic lake. Benthic dissolved oxygen concentrations were significantly lower (p-value < 0.001) at sites with N. obtusa compared to sites without N. obtusa. Additionally, N. obtusa biomass was a negative predictor of near-bed oxygen concentration (R2 = 0.59, p-value < 0.001). Knowing that anoxia can promote the internal loading of phosphorus, we measured soluble reactive phosphorus (SRP) in the pore-water of sediments at each site, and found N. obtusa biomass explained 90% of sediment pore-water SRP (R2 = 0.90, p-value < 0.001). These notable associations between N. obtusa and key lake elements indicates that N. obtusa may be acting as an ecosystem engineer in invaded lakes by altering the biogeochemical fate of oxygen and phosphorus.

Comparison of physicochemical properties and selective catalytic reduction activities of CeMn/TiO2 catalysts with and without phosphorus additives

Lubricant additives contain phosphorus, which has a fly ash effect. Phosphorus negatively affects catalyst activity. Determining the effects of phosphorus loading amount on the catalytic activity is important for the development of catalysts with high NOx reduction. This study focuses on the control of NOx emissions, one of the air pollutants released from the diesel engine. The catalysts used in the reduction of NOx emissions were synthesized by washcoating method. Ce and Mn contents of all catalysts were adjusted as 3%, while the phosphorus contents of poisoned catalysts were adjusted as 0.5% and 1%. For this purpose, cordierite with high surface area was used. The catalysts were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Brunauer-Emmett-Teller (BET), X-Ray diffraction (XRD) and ultraviolet visible spectroscopy (UV-Vis) analyzes. The NOx reduction activity of with and without phosphorus doped CeMn/TiO2 catalysts was investigated with the designed selective catalytic reduction system (SCR). NOx conversion ratios of the CeMn/TiO2 catalyst reached the high values of 84.6% at 280°C. After the phosphorus loading, the structure of the CeMn/TiO2 catalyst deteriorated, and the NOx conversion ratios decreased. 0.5P-CeMn/TiO2 and 1P-CeMn/TiO2 catalysts showed lower NOx conversion ratios compared to CeMn/TiO2 catalyst. CeMn-TiO2 catalyst was found highly active for SCR at all tests. Phosphorus loading caused deactivation of the catalyst and deactivation increased due to the increase in phosphorus loading amount.