Short-term changes in phosphorus storage in an oligotrophic Everglades wetland ecosystem receiving experimental nutrient enrichment

Natural, unenriched Everglades wetlands are known to be limited by phosphorus (P) and responsive to P enrichment. However, whole-ecosystem evaluations of experimental P additions are rare in Everglades or other wetlands. We tested the response of the Everglades wetland ecosystem to continuous, low-level additions of P (0, 5, 15, and 30 μg L−1 above ambient) in replicate, 100 m flow-through flumes located in unenriched Everglades National Park. After the first six months of dosing, the concentration and standing stock of phosphorus increased in the surface water, periphyton, and flocculent detrital layer, but not in the soil or macrophytes. Of the ecosystem components measured, total P concentration increased the most in the floating periphyton mat (30 μg L−1: mean = 1916 μg P g−1, control: mean = 149 μg P g−1), while the flocculent detrital layer stored most of the accumulated P (30 μg L−1: mean = 1.732 g P m−2, control: mean = 0.769 g P m−2). Significant short-term responses of P concentration and standing stock were observed primarily in the high dose (30 μg L−1 above ambient) treatment. In addition, the biomass and estimated P standing stock of aquatic consumers increased in the 30 and 5 μg L−1 treatments. Alterations in P concentration and standing stock occurred only at the upstream ends of the flumes nearest to the point source of added nutrient. The total amount of P stored by the ecosystem within the flume increased with P dosing, although the ecosystem in the flumes retained only a small proportion of the P added over the first six months. These results indicate that oligotrophic Everglades wetlands respond rapidly to short-term, low-level P enrichment, and the initial response is most noticeable in the periphyton and flocculent detrital layer.

Ecosystem Structure and Function Still Altered Two Decades After Short-Term Fertilization of a Seagrass Meadow

An oligotrophic phosphorus (P) limited seagrass ecosystem in Florida Bay was experimentally fertilized in a unique way. Perches were installed to encourage seabirds to roost and deliver an external source of nutrients via defecation. Two treatments were examined: (1) a chronic 23-year fertilization and (2) an earlier 28-month fertilization that was discontinued when the chronic treatment was initiated. Because of the low mobility of P in carbonate sediments, we hypothesized long-term changes to ecosystem structure and function in both treatments. Structural changes in the chronic treatment included a shift in the dominant seagrass species from Thalassia testudinum to Halodule wrightii, large increases in epiphytic biomass and sediment chlorophyll-a, and a decline in species richness. Functional changes included increased benthic metabolism and quantum efficiency. Initial changes in the 28-month fertilization were similar, but after 23 years of nutrient depuration T. testudinum has reestablished itself as the dominant species. However, P remains elevated in the sediment and H. wrightii has maintained a presence. Functionally the discontinued treatment remains altered. Biomass exceeds that in the chronic treatment and indices of productivity, elevated relative to control, are not different from the chronic fertilization. Cessation of nutrient loading has resulted in a superficial return to the pre-disturbance character of the community, but due to the nature of P cycles functional changes persist.

Short-term changes in phosphorus storage in an oligotrophic Everglades wetland ecosystem receiving experimental nutrient enrichment

Natural, unenriched Evergladeswetlands are known to be limited by phosphorus(P) and responsive to P enrichment. However,whole-ecosystem evaluations of experimental Padditions are rare in Everglades or otherwetlands. We tested the response of theEverglades wetland ecosystem to continuous,low-level additions of P (0, 5, 15, and30 μg L−1 above ambient) in replicate,100 m flow-through flumes located in unenrichedEverglades National Park. After the first sixmonths of dosing, the concentration andstanding stock of phosphorus increased in thesurface water, periphyton, and flocculentdetrital layer, but not in the soil or macrophytes. Of the ecosystem components measured, total P concentration increased the most in the floating periphyton mat (30 μg L−1: mean = 1916 μg P g−1, control: mean =149 μg P g−1), while the flocculentdetrital layer stored most of the accumulated P(30 μg L−1: mean = 1.732 g P m−2,control: mean = 0.769 g P m−2). Significant short-term responsesof P concentration and standing stock wereobserved primarily in the high dose (30 μgL−1 above ambient) treatment. Inaddition, the biomass and estimated P standingstock of aquatic consumers increased in the 30and 5 μg L−1 treatments. Alterationsin P concentration and standing stock occurredonly at the upstream ends of the flumes nearestto the point source of added nutrient. Thetotal amount of P stored by the ecosystemwithin the flume increased with P dosing,although the ecosystem in the flumes retainedonly a small proportion of the P added over thefirst six months. These results indicate thatoligotrophic Everglades wetlands respondrapidly to short-term, low-level P enrichment,and the initial response is most noticeable inthe periphyton and flocculent detrital layer.

Patterns and effects of notetaking by learning -disabled and nondisabled adolescents: A comparative study

This study analyzes the qualitative and quantitative patterns of notetaking by learning disabled (LD) and nondisabled (ND) adolescents and the effectiveness of notetaking and review as measured by the subjects' ability to recall information presented during a lecture. The study also examines relationships between certain learner characteristics and notetaking. The following notetaking variables were investigated: note completeness, number of critical ideas recorded, levels of processing information, organizational strategies, fluency of notes, and legibility of notes. The learner characteristics examined pertained to measures on achievement, short-term memory, listening comprehension, and verbal ability.^ Students from the 11th and 12th grades were randomly selected from four senior high schools in Dade County, Florida. Seventy learning disabled and 79 nondisabled subjects were shown a video tape lecture and required to take notes. The lecture conditions controlled for presentation rate, prior knowledge, information density, and difficulty level. After 8 weeks, their notes were returned to the subjects for a review period, and a posttest was administered.^ Results of this study suggest significant differences (p $\le$.01) in the patterns of notetaking between LD and ND groups not due to differences in the learner characteristics listed above. In addition, certain notetaking variables such as process levels, number of critical ideas, and note completeness were found to be significantly correlated to learning outcome. Further, deficiencies in the spontaneous use of organizational strategies and abbreviations adversely affected the notetaking effectiveness of learning disabled students.^ Both LD and ND subjects recalled more information recorded in their notes than not recorded. This difference was significant only for the ND group. By contrast, LD subjects compensated for their poor notetaking skills and recalled significantly more information not recorded on their notes than did ND subjects. The major implications of these findings suggest that LD and ND subjects exhibit very different entry behaviors when asked to perform a notetaking task; hence, teaching approaches to notetaking must differ as well. ^