114 lakes treated with aluminum (Al) salts to reduce internal phosphorus (P) loading were analyzed to identify factors driving longevity of post-treatment water quality improvements. Lakes varied greatly in morphology, applied Al dose, and other factors that may have affected overall treatment effectiveness. Treatment longevity based on declines in epilimnetic total P (TP) concentration averaged 11 years for all lakes (range of 0-45 years). When longevity estimates were used for lakes with improved conditions through the end of measurements, average longevity increased to 15 years. Significant differences in treatment longevity between deeper, stratified lakes (mean 21 years) and shallow, polymictic lakes (mean 5.7 years) were detected, indicating factors related to lake morphology are important for treatment success. A decision tree developed using a partition model suggested Al dose, Osgood index (OI, a morphological index), and watershed to lake area ratio (related to hydraulic residence time, WA:LA) were the most important variables determining treatment longevity. Multiple linear regression showed that Al dose, WA:LA, and OI explained 47, 32 and 3% respectively of the variation in treatment longevity. Other variables (too data limited to include in the analysis) also appeared to be of importance, including sediment P content to Al dose ratios and the presence of benthic feeding fish in shallow, polymictic lakes.

We present an analysis of long-term (1988-2013; 26years) total phosphorus (TP) concentration trends in 81 Swedish boreal lakes subject to minimal anthropogenic disturbance. Near universal increases in dissolved organic carbon (DOC) concentrations and a widespread but hitherto unexplained decline in TP were observed. Over 50% of the lakes (n=42) had significant declining TP trends over the past quarter century (Sen's slope=2.5%y). These declines were linked to catchment processes related to changes in climate, recovery from acidification, and catchment soil properties, but were unrelated to trends in P deposition. Increasing DOC concentrations appear to be masking in-lake TP declines. When the effect of increasing DOC was removed, the small number of positive TP trends (N=5) turned negative and the average decline in TP increased to 3.9%y. The greatest relative TP declines occurred in already nutrient poor, oligotrophic systems and TP concentrations have reached the analytical detection limit (1μgL) in some lakes. In addition, ongoing oligotrophication may be exacerbated by increased reliance on renewable energy from forest biomass and hydropower. It is a cause of significant concern that potential impairments to lake ecosystem functioning associated with oligotrophication are not well handled by a management paradigm focused exclusively on the negative consequences of increasing phosphorus concentrations.

Abstract-The effectiveness of aluminum (Al) at retaining phosphate was investigated in alum-treated Washington lake sediments. Greater than background concentrations of Al and Al-bound phosphorus (Al-P) were detected in three stratified lakes (Lake Ballinger, Phantom Lake, and Medical Lake) and in three unstratified lakes (Lake Erie, Cambell Lake, and Long Lake). The ratio of added Al to P (Al : Al-P) was approximately 11 : 1 by weight in all six lakes. Added Al ranged from 6 to 83 g Al m Ϫ2 , and adsorbed P subsequently ranged from 0.5 to 7.3 g P m Ϫ2 . P bound to the added Al was apparently removed from the P cycle, as the layers of increased Al-P due to treatment were buried in the sediment at a depth corresponding to the approximate time since treatment.Sediments provide the only significant phosphorus (P) sink in lakes and are thus an important regulator of trophic status. Part of the P deposited on the sediment surface will be recycled to the water column, and the internal cycling of P is regulated by both biotic and abiotic factors (Boström et al. 1982(Boström et al. , 1988. The ultimate fate of P, however, in terms of permanent removal from the P cycle, is determined by the capacity of anoxic sediments to retain the buried P (Lijklema 1994). The input and accumulation of different adsorbents to the sediments is thus equally important to its P-retention capacity as the P input for the retaining capacity of the sediment (Lijklema 1994). Ferric iron (Fe) is the primary active P-retaining compound in fresh waters where the ratio between available Fe and P will determine the adsorption efficiency (Jensen et al. 1992). This adsorption capacity is drastically reduced under anoxic conditions (Mortimer 1941(Mortimer , 1942. The chemistry of phosphate in sediments is also closely connected to aluminum (Al) and to a lesser extent calcium (Boers et al. 1993).For three decades Al (usually alum) has been used in North America and Europe to inactivate phosphate migrating from lake sediments regardless the redox status. Although frequently used, the longevity of treatments has ranged from Ͻ1-20 yr, averaging about 10 (Welch and Cooke 1999). This variation may be dependent on the dose of Al added and the resulting amount of formed Al-P, or the dissolution of formed Al-P with time. However, data are lacking on Pretention capacity of Al in situ (Cooke et al. 1993;Welch and Cooke 1999). Data on strong adsorbents that permanently bind P, in order to explain differences in burial rate of P, are also very limited (Boers et al. 1993). This type of information is needed to predict effectiveness/longevity of lake restoration projects where Al is added to adsorb P in the sediment. Alum treatments, where both the Al dose and the time of application are known, provide an opportunity to evaluate the P-sorption capacity in situ of Al, based on the ratio of Al to Al-P and the resistance of Al-P to early sediment diagenesis.The objective of this work was to quantify the effects of Al on the P cycle by determining concentrations of A...

Abstract. Long term data series (1996 through 2009) for trace metals were analyzed from a large number of streams and rivers across Sweden varying in tributary watershed size from 0.05 to 48 193 km 2 . The final data set included 139 stream sites with data for arsenic (As), cobalt (Co), copper (Cu), chromium (Cr), nickel (Ni), lead (Pb), zinc (Zn), and vanadium (V). Between 7 % and 46 % of the sites analyzed showed significant trends according to the seasonal Kendall test. However, in contrast to previous studies and depositional patterns, a substantial portion of the trends were positive, especially for V (100 %), As (95 %), and Pb (68 %). Other metals (Zn and Cr) generally decreased, were mixed (Ni and Zn), or had very few trends (Co) over the study period. Trends by region were also analyzed and some showed significant variation between the north and south of Sweden. Regional trends for both Cu and Pb were positive (60 % and 93 %, respectively) in the southern region but strongly negative (93 % and 75 %, respectively) in the northern region. Kendall's τ coefficients were used to determine dependence between metals and potential in-stream drivers including total organic carbon (TOC), iron (Fe), pH, and sulphate (SO 2− 4 ). TOC and Fe correlated positively and strongly with As, V, Pb, and Co while pH and SO 2− 4 generally correlated weakly, or not at all with the metals studied.

There is a pressing need to apply stability and resilience theory to environmental management to restore degraded ecosystems effectively and to mitigate the effects of impending environmental change. Lakes represent excellent model case studies in this respect and have been used widely to demonstrate theories of ecological stability and resilience that are needed to underpin preventative management approaches. However, we argue that this approach is not yet fully developed because the pursuit of empirical evidence to underpin such theoretically grounded management continues in the absence of an objective probability framework. This has blurred the lines between intuitive logic (based on the elementary principles of probability) and extensional logic (based on assumption and belief) in this field.