Melanie A. Riedinger-Whitmore

Chapter 2 – Mid-Holocene climate and culture change in coastal Peru

Publisher Summary This chapter reviews the history of study and the current status of Mid-Holocene climatic and cultural change along the Peruvian coast, with a focus on major transitions at ca. 5800 and 3000 cal yr BP that correlate temporally with changes in El Nino Southern Oscillation (ENSO) frequency. It begins with presenting the Peruvian archaeological record of Holocene El Nino frequency variation, considering several hypotheses to explain the data. Based on the archaeological record, it is concluded that for some time prior to 5800 years ago, the coast of Peru, north of 10°S latitude, was characterized by permanent warm water. From these data, it is hypothesized that El Nino did not operate for some period before 5800 cal yr BP; after that time, conditions as essentially the same as today were seen. Present-day climatic variability on interannual time scales in the tropics is dominated by ENSO, which involves both the atmosphere and the ocean in the tropical Pacific (e.g., Maasch, in press). Through teleconnections, extratropical climatic variability on these time scales is also impacted by ENSO. Continuous natural Holocene paleoclimate archives from northern Peru, Ecuador, and the eastern tropical Pacific Ocean are difficult to find, privileging anthropogenic deposits from archaeological sites. Although precisely dating these records is difficult, climatic change determined from them is consistent. The regional paleoclimate records are presented.

Cyanobacterial Proliferation is a Recent Response to Eutrophication in Many Florida Lakes: A Paleolimnological Assessment

Abstract Cyanobacteria dominate many highly productive Florida lakes. Algal proliferation often is attributed to eutrophication during the last century, but it is poorly documented because Floridas water-quality monitoring programs became common only after 1980. We interpret paleolimnological data from the sediment cores of 6 productive lakes to determine when cyanobacterial proliferation first occurred, and whether it resulted from natural edaphic influence or from eutrophication caused by human activities. Major algal-pigment groups in sediments were analyzed using pigment-extraction and spectrophotometric techniques. Pigment profiles are compared with WACALIB-derived inferences for limnetic total-P, limnetic chlorophyll a, and trophic-state index values based on sedimented diatoms, and with stable isotope (δ13C & δ15N) signatures of organic matter. Cyanobacterial and algal proliferation increased during recent decades in 5 of the 6 study lakes in response to eutrophication. Two lakes demonstrated some evidence of recovery following nutrient-mitigation programs that reduced sewage and other point-source inputs. Five lakes showed intermittent to moderate cyanobacteria presence in the bottom portion of their cores because of edaphic nutrient supply or early watershed disturbance. One highly productive lake showed no evidence of eutrophication and demonstrated that dense cyanobacterial populations can occur naturally. Relationships were particularly strong among sedimented pigment profiles and diatom-inferred limnetic water-quality profiles. Although cyanobacteria have long-standing presence in some naturally productive Florida lakes, our studies suggest that algal proliferation in many lakes is both recent and abrupt in response to eutrophication. Paleolimnological methods are informative about the timing and causes of cyanobacterial appearance in regions where long-term water-quality data are lacking.

Tropical Pacific climate variability over the last 6000 years as recorded in Bainbridge Crater Lake, Galápagos

National Science Foundation (NSF) RAPID, Program [AGS-1256970, AGS-1561121]; NOAA Climate Program Office; University of Arizona Department of Geosciences; Philanthropic Education Organization; National Science Foundation (NSF) P2C2, Program [AGS-1256970, AGS-1561121]; National Science Foundation (NSF) Geospace Sciences Paleoclimate Program [AGS-1256970, AGS-1561121]

Using palaeoecological and palaeoenvironmental records to guide restoration, conservation and adaptive management of Ramsar freshwater wetlands: lessons from the Everglades, USA

The Everglades, the largest Ramsar wetland in the USA, is a spatially complex mosaic of freshwater habitats heavily impacted by agriculture, urban land use, and efforts to manage water resources in southern Florida. Restoration and conservation of these habitats is challenging because they experience different threats, and require different water levels, hydroperiods and disturbances. Historically, Everglades hydrology was maintained by seasonal precipitation and surface-water flows, but was significantly altered in the 20th century to foster agriculture and urban growth. Everglades palaeoecological and palaeoenvironmental studies provide opportunities to examine spatial and temporal variability in wetland conditions, and document past climate and anthropogenic influences on plant succession and habitat persistence since the mid-Holocene. This paper summarises key Everglades palaeoecological and palaeoenvironmental research, and highlights lessons learned about the evolution of the ecosystem, historical variability, and natural and anthropogenic influences. These lessons have been used in defining reference conditions and community targets in current efforts to restore the Everglades. Palaeoenvironmental and palaeoecological studies enhance our understanding about properties that define and contribute to the ecological character of wetlands, and they can identify criteria that are important for restoration and conservation projects in Ramsar-listed wetlands.

Limnetic total phosphorus transfer functions for lake management: considerations about their design, use, and effectiveness

Regulatory agencies often rely on paleolimnological studies for models that predict variables pertinent to nutrient loading or to public perception. Limitations of statistical approaches often pose significant challenges. We present a case study from Florida USA that involves diatom-based inference models derived from two calibration sets. Spatial autocorrelation conclusions differed with methods and approaches, and h block cross validation was unduly pessimistic. Calibration sets and temporal sets represent fundamentally different populations. The accuracy and precision of temporal inferences for specific lakes can be affected by site-specific factors, and are not likely to be known with the certainty suggested by models. Error terms can provide a false sense of knowledge about the reliability of inferences for temporal samples. Broad error terms for limnetic total phosphorus models have little or no utility in any event. Limnetic total P models can perform poorly when applied to N-limited lakes. Transfer functions should be regarded more as qualitative indicators of past water quality rather than methods with known precision, and more emphasis should be placed on multiple lines of evidence and ecological interpretations.

Cyanobacterial influence on diatom community lifeform dynamics in shallow subtropical lakes of Florida USA.

Fragilarioid diatom taxa are often deemed ubiquitous in shallow lake systems. Their presence has been described as contributing to statistical noise in paleolimnological studies of cold-temperate lakes. In shallow, warm-temperate lakes of Florida, long-term transitions from assemblages dominated by Aulacoseira spp. to fragilarioid taxa, particularly Pseudostaurosira brevistriata, Staurosira construens var. venter, and Staurosirella pinnata, often occur. Distinctly higher limnetic nutrient optima are demonstrated by these fragilarioid taxa than by planktonic Aulacoseira spp. Community successions occur during eutrophication, and progressive replacement of Aulacoseira spp. and other planktonic taxa by fragilarioid taxa is concurrent with and apparently related to the onset of cyanobacterial dominance. We examine successions from Aulacoseira-dominated to fragilarioid-dominated assemblages in sediment cores from subtropical Florida lakes that have undergone eutrophication. Diatom profiles are compared with sedimented pigments, nitrogen stable isotopes of organic matter, and with silica accumulation rates. These study lakes have little if any macrophyte presence. Their light-extinction depths are extremely shallow, yet diatom communities are dominated by bottom-dwelling rather than planktonic taxa. Frequent wind-generated mixing, sometimes to lake bottoms, is sufficient to sustain the light needs of benthic and tychoplanktonic taxa. We conclude that assemblage changes generally are not caused by reduced water depths, silica limitation, nor increased incipient stratification, but that cyanobacteria are responsible for reducing planktonic Aulacoseira in favor of fragilarioid taxa. Cyanobacteria blooms persist over a wide seasonal range because of warm climate and high limnetic nutrient concentrations in Florida lakes. Cyanobacteria progressively displace and outcompete Aulacoseira and other planktonic taxa as eutrophication proceeds. Reduced light availability, changes in mineral/nutrient availability, and other aspects of competitive exclusion, such as cyanobacterial allelotoxins, might contribute to observed changes. Climate warming is not likely to account for Aulacoseira reduction as in colder regions because it is less pronounced in this subtropical district. Lakes with low nutrient levels and less cyanobacteria still sustain large Aulacoseira populations, and decreases in limnetic nutrients sometimes lead to the return of planktonic Aulacoseira. Rather than simply representing statistical noise for paleolimnological reconstructions, shifts to certain fragilarioid taxa indicate when subtropical Florida lakes progressed to hypereutrophic conditions that were marked by cyanobacterial proliferation.